From 7b6b24b9c5b777129b861edad6c845394b592eba Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Fri, 22 May 2026 03:29:18 +0900
Subject: [PATCH 1/7] #351

---
 backend/app/controllers/posts_controller.rb   | 67 ++++++++++++++-----
 backend/app/models/post.rb                    | 33 ++++++++-
 backend/app/models/post_tag.rb                |  6 ++
 backend/app/models/post_tag_section.rb        | 20 ++++++
 backend/app/models/tag.rb                     | 46 ++++++++++++-
 ...20260518235300_create_post_tag_sections.rb | 19 ++++++
 .../20260519013100_add_video_ms_to_posts.rb   |  9 +++
 backend/db/schema.rb                          | 21 +++++-
 backend/spec/models/post_tag_spec.rb          | 29 ++++++++
 frontend/src/components/PostEditForm.tsx      |  5 +-
 frontend/src/lib/utils.ts                     | 12 ++++
 .../deerjikists/DeerjikistDetailPage.tsx      |  6 ++
 frontend/src/types.ts                         |  7 +-
 13 files changed, 255 insertions(+), 25 deletions(-)
 create mode 100644 backend/app/models/post_tag_section.rb
 create mode 100644 backend/db/migrate/20260518235300_create_post_tag_sections.rb
 create mode 100644 backend/db/migrate/20260519013100_add_video_ms_to_posts.rb
 create mode 100644 backend/spec/models/post_tag_spec.rb

diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index e8cae00..96f520c 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -95,9 +95,10 @@ class PostsController < ApplicationController
   end
 
   def random
-    post = filtered_posts.preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
-                         .order('RAND()')
-                         .first
+    post = filtered_posts
+           .preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+           .order('RAND()')
+           .first
     return head :not_found unless post
 
     render json: PostRepr.base(post, current_user)
@@ -108,7 +109,7 @@ class PostsController < ApplicationController
     return head :not_found unless post
 
     render json: PostRepr.base(post, current_user)
-                         .merge(tags: build_tag_tree_for(post.tags),
+                         .merge(tags: build_tag_tree_for(post),
                                 related: PostRepr.many(post.related(limit: 20)))
   end
 
@@ -132,11 +133,11 @@ class PostsController < ApplicationController
     ApplicationRecord.transaction do
       post.save!
 
-      tags = Tag.normalise_tags!(tag_names)
+      Tag.normalise_tags!(tag_names, with_sections: true) => { tags:, sections: }
       TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
 
       tags = Tag.expand_parent_tags(tags)
-      sync_post_tags!(post, tags)
+      sync_post_tags!(post, tags, sections)
 
       sync_parent_posts!(post, parent_post_ids)
 
@@ -235,7 +236,7 @@ class PostsController < ApplicationController
 
     post.reload
     json = PostRepr.base(post, current_user)
-    json['tags'] = build_tag_tree_for(post.tags)
+    json['tags'] = build_tag_tree_for(post)
     render json:, status: :ok
   rescue Tag::NicoTagNormalisationError
     head :bad_request
@@ -337,7 +338,7 @@ class PostsController < ApplicationController
   def tagged_post_ids_for(name) =
       Post.joins(tags: :tag_name).where(tag_names: { name: }).select(:id)
 
-  def sync_post_tags! post, desired_tags
+  def sync_post_tags! post, desired_tags, sections
     desired_tags.each do |t|
       t.save! if t.new_record?
     end
@@ -356,13 +357,20 @@ class PostsController < ApplicationController
       end
     end
 
+    PostTagSection.where(post_id: post.id).destroy_all
+    sections.each do |tag_id, ranges|
+      ranges.each do |begin_ms, end_ms|
+        PostTagSection.create!(post_id: post.id, tag_id:, begin_ms:, end_ms:)
+      end
+    end
+
     PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
       pt.discard_by!(current_user)
     end
   end
 
-  def build_tag_tree_for tags
-    tags = tags.to_a
+  def build_tag_tree_for post
+    tags = post.tags.to_a
     tag_ids = tags.map(&:id)
 
     implications = TagImplication.where(parent_tag_id: tag_ids, tag_id: tag_ids)
@@ -384,8 +392,11 @@ class PostsController < ApplicationController
       tag = tags_by_id[tag_id]
       return nil unless tag
 
+      sections = PostTagSection.where(post_id: post.id, tag_id: tag.id)
+                 .as_json(only: [:begin_ms, :end_ms])
+
       if path.include?(tag_id)
-        return TagRepr.base(tag).merge(children: [])
+        return TagRepr.base(tag).merge(children: [], sections:)
       end
 
       if memo.key?(tag_id)
@@ -397,7 +408,7 @@ class PostsController < ApplicationController
 
       children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
 
-      memo[tag_id] = TagRepr.base(tag).merge(children:)
+      memo[tag_id] = TagRepr.base(tag).merge(children:, sections:)
     end
 
     root_ids.filter_map { |id| build_node.call(id, []) }
@@ -470,7 +481,21 @@ class PostsController < ApplicationController
   end
 
   def editable_tag_names_from_post post
-    post.tags.not_nico.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+    post
+        .post_tags
+        .kept
+        .joins(tag: :tag_name)
+        .merge(Tag.not_nico)
+        .includes(:sections, tag: :tag_name)
+        .order('tag_names.name')
+        .map do |post_tag|
+      name = post_tag.tag.tag_name.name
+      sections = post_tag.sections.sort_by(&:begin_ms)
+
+      next name if sections.empty?
+
+      "#{ name }#{ sections.map { Post.section_literal(_1) }.join }"
+    end
   end
 
   def post_incoming_snapshot title:, original_created_from:, original_created_before:,
@@ -502,9 +527,16 @@ class PostsController < ApplicationController
   end
 
   def incoming_tag_names_for_snapshot raw_tag_names
-    tags = Tag.normalise_tags!(raw_tag_names, with_tagme: false)
+    Tag.normalise_tags!(raw_tag_names, with_tagme: false, with_sections: true) =>
+        { tags:, sections: }
 
-    Tag.expand_parent_tags(tags).map(&:name).uniq.sort
+    Tag.expand_parent_tags(tags).uniq(&:id).map { |tag|
+      "#{ tag.name }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
+    }.sort
+  end
+
+  def section_literal section
+    "[#{ Post.ms_to_time(section[0]) }-#{ Post.ms_to_time(section[1]) }]"
   end
 
   def post_conflict_json post:, base_version_no:, base_snapshot:,
@@ -591,7 +623,8 @@ class PostsController < ApplicationController
                  original_created_from: snapshot[:original_created_from],
                  original_created_before: snapshot[:original_created_before])
 
-    editable_tags = Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false)
+    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false, with_sections: true) =>
+        { tags: editable_tags, sections: }
     TagVersioning.record_tag_snapshots!(editable_tags, created_by_user: current_user)
 
     readonly_tags = post.tags.nico.to_a
@@ -599,7 +632,7 @@ class PostsController < ApplicationController
     tags = readonly_tags + editable_tags
     tags = Tag.expand_parent_tags(tags)
 
-    sync_post_tags!(post, tags)
+    sync_post_tags!(post, tags, sections)
     sync_parent_posts!(post, snapshot[:parent_post_ids])
 
     PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 4c3ddb1..8970119 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -56,7 +56,38 @@ class Post < ApplicationRecord
     super(options).merge(thumbnail: nil)
   end
 
-  def snapshot_tag_names = tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  def snapshot_tag_names
+    post_tags
+        .kept
+        .joins(tag: :tag_name)
+        .includes(:sections, tag: :tag_name)
+        .order('tag_names.name')
+        .map do |post_tag|
+      name = post_tag.tag.tag_name.name
+      sections = post_tag.sections.sort_by(&:begin_ms)
+
+      next name if sections.empty?
+
+      "#{ name }#{ sections.map { Post.section_literal(_1) }.join }"
+    end
+  end
+
+  def self.section_literal section
+    "[#{ Post.ms_to_time(section.begin_ms) }-#{ Post.ms_to_time(section.end_ms) }]"
+  end
+
+  def self.ms_to_time ms
+    total_s = ms / 1_000
+    s = total_s % 60
+    min = (total_s / 60) % 60
+    h = total_s / 3_600
+
+    if h.positive?
+      '%d:%02d:%02d' % [h, min, s]
+    else
+      '%d:%02d' % [min, s]
+    end
+  end
 
   def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
 
diff --git a/backend/app/models/post_tag.rb b/backend/app/models/post_tag.rb
index 702f66a..ac56c77 100644
--- a/backend/app/models/post_tag.rb
+++ b/backend/app/models/post_tag.rb
@@ -10,6 +10,12 @@ class PostTag < ApplicationRecord
   belongs_to :created_user, class_name: 'User', optional: true
   belongs_to :deleted_user, class_name: 'User', optional: true
 
+  has_many :sections, -> { order(:begin_ms) }, class_name: 'PostTagSection',
+                                               foreign_key: [:post_id, :tag_id],
+                                               primary_key: [:post_id, :tag_id],
+                                               dependent: :delete_all,
+                                               inverse_of: :post_tag
+
   validates :post_id, presence: true
   validates :tag_id, presence: true
   validates :post_id, uniqueness: {
diff --git a/backend/app/models/post_tag_section.rb b/backend/app/models/post_tag_section.rb
new file mode 100644
index 0000000..8d6af9e
--- /dev/null
+++ b/backend/app/models/post_tag_section.rb
@@ -0,0 +1,20 @@
+class PostTagSection < ApplicationRecord
+  self.primary_key = :post_id, :tag_id, :begin_ms
+
+  belongs_to :post
+  belongs_to :tag
+
+  belongs_to :post_tag, -> { kept }, foreign_key: [:post_id, :tag_id],
+                                     primary_key: [:post_id, :tag_id],
+                                     inverse_of: :sections,
+                                     optional: true
+
+  validates :post_id, presence: true
+  validates :tag_id, presence: true
+
+  validates :begin_ms, presence: true,
+                       numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+
+  validates :end_ms, presence: true,
+                     numericality: { only_integer: true, greater_than: :begin_ms }
+end
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 51ca783..0015250 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -92,22 +92,45 @@ class Tag < ApplicationRecord
 
   def self.normalise_tags! tag_names, with_tagme: true,
                                       with_no_deerjikist: true,
-                                      deny_nico: true
+                                      deny_nico: true,
+                                      with_sections: false
     if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
       raise NicoTagNormalisationError
     end
 
+    sections = { }
     tags = tag_names.map do |name|
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
+
       name = TagName.canonicalise(name.sub(/\A#{ pf }/i, '')).first
+
+      sections_by_tag = []
+      while n = name.sub!(/^(\S*?)\[([0-9:.]*?)-([0-9:.]*?)\](\S*?)$/, '\1\4 \2 \3')
+        name, *section_raw = n.split
+
+        begin_ms, end_ms = section_raw.map { time_to_ms(_1) }
+        next if begin_ms == end_ms
+
+        begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
+
+        sections_by_tag << [begin_ms, end_ms]
+      end
+
       find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         tag.update!(category: cat) if cat && tag.category != cat
+        sections[tag.id] = sections_by_tag if sections_by_tag.present?
       end
     end
 
     tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
     tags << Tag.no_deerjikist if with_no_deerjikist && tags.all? { |t| !(t.deerjikist?) }
-    tags.uniq(&:id)
+    tags.uniq!(&:id)
+
+    if with_sections
+      { tags:, sections: }
+    else
+      tags
+    end
   end
 
   def self.expand_parent_tags tags
@@ -228,4 +251,23 @@ class Tag < ApplicationRecord
       errors.add :category, 'ニジラーと紐づいてゐるタグはニジラー・カテゴリである必要があります．'
     end
   end
+
+  def self.time_to_ms str
+    parts = str.split(':')
+
+    s_part = parts.pop
+    s, ms = s_part.split('.')
+
+    total_s = s.to_i
+
+    if parts.length >= 1
+      total_s += parts.pop.to_i * 60
+    end
+
+    if parts.length >= 1
+      total_s += parts.pop.to_i * 3_600
+    end
+
+    total_s * 1_000 + ms.to_s.ljust(3, '0')[0, 3].to_i
+  end
 end
diff --git a/backend/db/migrate/20260518235300_create_post_tag_sections.rb b/backend/db/migrate/20260518235300_create_post_tag_sections.rb
new file mode 100644
index 0000000..ff87e20
--- /dev/null
+++ b/backend/db/migrate/20260518235300_create_post_tag_sections.rb
@@ -0,0 +1,19 @@
+class CreatePostTagSections < ActiveRecord::Migration[8.0]
+  def change
+    create_table :post_tag_sections, primary_key: [:post_id, :tag_id, :begin_ms] do |t|
+      t.references :post, null: false, foreign_key: true, index: false
+      t.references :tag, null: false, foreign_key: true, index: false
+      t.integer :begin_ms, null: false
+      t.integer :end_ms, null: false
+      t.timestamps
+
+      t.index [:post_id, :begin_ms], name: 'idx_post_tag_sections_post_id_begin_ms'
+
+      t.check_constraint 'begin_ms >= 0',
+                         name: 'chk_post_tag_sections_begin_ms_natural'
+
+      t.check_constraint 'begin_ms < end_ms',
+                         name: 'chk_post_tag_sections_end_ms_after_begin_ms'
+    end
+  end
+end
diff --git a/backend/db/migrate/20260519013100_add_video_ms_to_posts.rb b/backend/db/migrate/20260519013100_add_video_ms_to_posts.rb
new file mode 100644
index 0000000..8225e13
--- /dev/null
+++ b/backend/db/migrate/20260519013100_add_video_ms_to_posts.rb
@@ -0,0 +1,9 @@
+class AddVideoMsToPosts < ActiveRecord::Migration[8.0]
+  def change
+    add_column :posts, :video_ms, :integer
+    add_index :posts, [:video_ms, :id], name: 'idx_posts_video_ms_id'
+
+    add_check_constraint :posts, 'video_ms IS NULL OR video_ms > 0',
+                         name: 'chk_posts_video_ms_positive'
+  end
+end
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index 94edb82..60e80eb 100644
--- a/backend/db/schema.rb
+++ b/backend/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
+ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -137,6 +137,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
     t.index ["target_post_id"], name: "index_post_similarities_on_target_post_id"
   end
 
+  create_table "post_tag_sections", primary_key: ["post_id", "tag_id", "begin_ms"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "post_id", null: false
+    t.bigint "tag_id", null: false
+    t.integer "begin_ms", null: false
+    t.integer "end_ms", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["post_id", "begin_ms"], name: "idx_post_tag_sections_post_id_begin_ms"
+    t.index ["tag_id"], name: "fk_rails_8be3847903"
+    t.check_constraint "`begin_ms` < `end_ms`", name: "chk_post_tag_sections_end_ms_after_begin_ms"
+    t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
+  end
+
   create_table "post_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
@@ -187,8 +200,11 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
     t.datetime "original_created_before"
     t.datetime "updated_at", null: false
     t.integer "version_no", null: false
+    t.integer "video_ms"
     t.index ["uploaded_user_id"], name: "index_posts_on_uploaded_user_id"
     t.index ["url"], name: "index_posts_on_url", unique: true
+    t.index ["video_ms", "id"], name: "idx_posts_video_ms_id"
+    t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_posts_video_ms_positive"
     t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
@@ -290,6 +306,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["expires_at"], name: "index_theatre_watching_users_on_expires_at"
+    t.index ["theatre_id", "expires_at"], name: "idx_on_theatre_id_skip_expires_at_4c8de1dd42"
     t.index ["theatre_id", "expires_at"], name: "index_theatre_watching_users_on_theatre_id_and_expires_at"
     t.index ["theatre_id"], name: "index_theatre_watching_users_on_theatre_id"
     t.index ["user_id"], name: "index_theatre_watching_users_on_user_id"
@@ -446,6 +463,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
   add_foreign_key "post_implications", "posts", column: "parent_post_id"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
+  add_foreign_key "post_tag_sections", "posts"
+  add_foreign_key "post_tag_sections", "tags"
   add_foreign_key "post_tags", "posts"
   add_foreign_key "post_tags", "tags"
   add_foreign_key "post_tags", "users", column: "created_user_id"
diff --git a/backend/spec/models/post_tag_spec.rb b/backend/spec/models/post_tag_spec.rb
new file mode 100644
index 0000000..551f3fd
--- /dev/null
+++ b/backend/spec/models/post_tag_spec.rb
@@ -0,0 +1,29 @@
+RSpec.describe PostTag, type: :model do
+  describe '#sections' do
+    it 'loads sections by post_id and tag_id' do
+      post_tag = create(:post_tag)
+      section = create(:post_tag_section,
+                       post: post_tag.post,
+                       tag: post_tag.tag,
+                       begin_ms: 1000,
+                       end_ms: 2000)
+
+      expect(post_tag.sections).to contain_exactly(section)
+    end
+
+    it 'does not load sections for another tag on the same post' do
+      post = create(:post)
+      tag = create(:tag)
+      other_tag = create(:tag)
+
+      post_tag = create(:post_tag, post:, tag:)
+      create(:post_tag_section,
+             post:,
+             tag: other_tag,
+             begin_ms: 1000,
+             end_ms: 2000)
+
+      expect(post_tag.sections).to be_empty
+    end
+  end
+end
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index bc1048e..4655f01 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -8,6 +8,7 @@ import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { isApiError } from '@/lib/api'
 import { updatePost } from '@/lib/posts'
+import { msToTime } from '@/lib/utils'
 
 import type { FC, FormEvent } from 'react'
 
@@ -25,7 +26,7 @@ const tagsToStr = (tags: Tag[]): string => {
 
   tags.filter (t => t.category !== 'nico').forEach (walk)
 
-  return [...(new Set (result.map (t => t.name)))].join (' ')
+  return [...(new Set (result.map (t => `${ t.name }${ t.sections.map (s => `[${ msToTime (s.beginMs) }-${ msToTime (s.endMs) }]`).join ('') }`)))].join (' ')
 }
 
 
@@ -167,4 +168,4 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
       </form>)
 }
 
-export default PostEditForm
\ No newline at end of file
+export default PostEditForm
diff --git a/frontend/src/lib/utils.ts b/frontend/src/lib/utils.ts
index aac3785..672ebd2 100644
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@@ -71,3 +71,15 @@ export const originalCreatedAtString = (
 	       .join (' '))
   return rtn === '〜' ? '年月日不詳' : rtn
 }
+
+
+export const msToTime = (ms: number): string => {
+  const totalS = Math.trunc (ms / 1_000)
+  const s = String (totalS % 60)
+  const min = String (Math.trunc (totalS / 60) % 60)
+  const h = String (Math.trunc (totalS / 3_600))
+
+  return (h > 0
+	  ? `${ h }:${ min.padStart (2, '0') }:${ s.padStart (2, '0') }`
+	  : `${ min }:${ s.padStart (2, '0') }`)
+}
diff --git a/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx b/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
index 69444b1..4901116 100644
--- a/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
+++ b/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
@@ -1,5 +1,6 @@
 import { useQuery, useQueryClient } from '@tanstack/react-query'
 import { useEffect, useMemo, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
 import { useParams } from 'react-router-dom'
 
 import TagLink from '@/components/TagLink'
@@ -69,6 +70,11 @@ const DeerjikistDetailPage: FC = () => {
 
   return (
       <MainArea>
+	<Helmet>
+	  <meta name="robots" content="noindex"/>
+	  {tag && <title>{tag.name} | ニジラー情報</title>}
+	</Helmet>
+
 	{(loading || !(tag)) ? 'Loading...' : (
 	    <div className="max-w-xl">
 	      <PageTitle>
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index e552f69..a4a7950 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -126,7 +126,7 @@ export type Post = {
     title:                  string | null
     thumbnail:              string | null
     thumbnailBase:          string | null
-    tags:                   Tag[]
+    tags:                   TagWithSections[]
     parentPosts?:           Post[]
     childPosts?:            Post[]
     siblingPosts?:          Record<`${ number }`, Post[]>
@@ -187,7 +187,6 @@ export type Tag = {
     hasWiki:        boolean
     materialId:     number | null
     hasDeerjikists: boolean
-    children?:      Tag[]
     matchedAlias?:  string | null }
 
 export type TagVersion = {
@@ -201,6 +200,10 @@ export type TagVersion = {
     createdAt:              string
     createdByUser:          { id: number; name: string | null } | null }
 
+export type TagWithSections = Tag & { sections: { beginMs:  number
+						  endMs:    number }[]
+			              children: TagWithSections[] }
+
 export type Theatre = {
     id:             number
     name:           string | null
-- 
2.34.1


From 7fcfc8b8aa8ca24a1fca3f4109ccd19a7e77c654 Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Sat, 23 May 2026 03:50:54 +0900
Subject: [PATCH 2/7] #351

---
 backend/app/controllers/posts_controller.rb  |  4 ++--
 backend/app/models/tag.rb                    |  9 +++++++--
 backend/spec/factories/post_tag_sections.rb  |  8 ++++++++
 backend/spec/factories/post_tags.rb          |  6 ++++++
 backend/spec/factories/posts.rb              |  8 ++++++++
 frontend/src/components/PostEditForm.tsx     | 17 ++++++++++-------
 frontend/src/components/TagDetailSidebar.tsx | 16 ++++++++--------
 frontend/src/lib/utils.ts                    |  2 +-
 frontend/src/pages/tags/TagDetailPage.tsx    |  2 +-
 frontend/src/test/factories.ts               |  6 ++++--
 10 files changed, 55 insertions(+), 23 deletions(-)
 create mode 100644 backend/spec/factories/post_tag_sections.rb
 create mode 100644 backend/spec/factories/post_tags.rb
 create mode 100644 backend/spec/factories/posts.rb

diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 96f520c..000577b 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -392,7 +392,7 @@ class PostsController < ApplicationController
       tag = tags_by_id[tag_id]
       return nil unless tag
 
-      sections = PostTagSection.where(post_id: post.id, tag_id: tag.id)
+      sections = PostTagSection.where(post_id: post.id, tag_id:)
                  .as_json(only: [:begin_ms, :end_ms])
 
       if path.include?(tag_id)
@@ -419,7 +419,7 @@ class PostsController < ApplicationController
 
     params[:parent_post_ids].to_s.split.map { |token|
       id = Integer(token, exception: false)
-      raise ArgumentError, "親投稿 Id. が不正です: #{ token }" if id.nil? || id <= 0
+      raise ArgumentError, "親投稿 Id. が不正です: #{ token }" if !(id) || id <= 0
 
       id
     }.uniq
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 0015250..f65ce24 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -102,7 +102,7 @@ class Tag < ApplicationRecord
     tags = tag_names.map do |name|
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
 
-      name = TagName.canonicalise(name.sub(/\A#{ pf }/i, '')).first
+      name = name.sub(/\A#{ pf }/i, '')
 
       sections_by_tag = []
       while n = name.sub!(/^(\S*?)\[([0-9:.]*?)-([0-9:.]*?)\](\S*?)$/, '\1\4 \2 \3')
@@ -116,9 +116,14 @@ class Tag < ApplicationRecord
         sections_by_tag << [begin_ms, end_ms]
       end
 
+      name = TagName.canonicalise(name).first
+
       find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         tag.update!(category: cat) if cat && tag.category != cat
-        sections[tag.id] = sections_by_tag if sections_by_tag.present?
+        next if sections_by_tag.blank?
+
+        sections[tag.id] ||= []
+        sections[tag.id].concat(sections_by_tag)
       end
     end
 
diff --git a/backend/spec/factories/post_tag_sections.rb b/backend/spec/factories/post_tag_sections.rb
new file mode 100644
index 0000000..2560395
--- /dev/null
+++ b/backend/spec/factories/post_tag_sections.rb
@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :post_tag_section do
+    association :post
+    association :tag
+    begin_ms { 1_000 }
+    end_ms { 2_000 }
+  end
+end
diff --git a/backend/spec/factories/post_tags.rb b/backend/spec/factories/post_tags.rb
new file mode 100644
index 0000000..6956ca3
--- /dev/null
+++ b/backend/spec/factories/post_tags.rb
@@ -0,0 +1,6 @@
+FactoryBot.define do
+  factory :post_tag do
+    association :post
+    association :tag
+  end
+end
diff --git a/backend/spec/factories/posts.rb b/backend/spec/factories/posts.rb
new file mode 100644
index 0000000..9f46b2e
--- /dev/null
+++ b/backend/spec/factories/posts.rb
@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :post do
+    sequence(:url) { |n| "https://example.com/factory-post-#{ n }" }
+    title { 'factory post' }
+    thumbnail_base { nil }
+    uploaded_user { nil }
+  end
+end
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 4655f01..2a2083e 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -12,21 +12,24 @@ import { msToTime } from '@/lib/utils'
 
 import type { FC, FormEvent } from 'react'
 
-import type { Post, Tag } from '@/types'
+import type { Post, TagWithSections } from '@/types'
 
 
-const tagsToStr = (tags: Tag[]): string => {
-  const result: Tag[] = []
+const tagsToStr = (tags: TagWithSections[]): string => {
+  const result: Omit<TagWithSections, 'children'>[] = []
 
-  const walk = (tag: Tag) => {
+  const walk = (tag: TagWithSections) => {
     const { children, ...rest } = tag
     result.push (rest)
-    children?.forEach (walk)
+    children.forEach (walk)
   }
 
   tags.filter (t => t.category !== 'nico').forEach (walk)
 
-  return [...(new Set (result.map (t => `${ t.name }${ t.sections.map (s => `[${ msToTime (s.beginMs) }-${ msToTime (s.endMs) }]`).join ('') }`)))].join (' ')
+  return [...(new Set (result.map (t =>
+      `${ t.name }${ t.sections
+		     .map (s => `[${ msToTime (s.beginMs) }-${ msToTime (s.endMs) }]`)
+		     .join ('') }`)))].join (' ')
 }
 
 
@@ -118,7 +121,7 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
   }
 
   useEffect (() => {
-    setTags(tagsToStr (post.tags))
+    setTags (tagsToStr (post.tags))
   }, [post])
 
   return (
diff --git a/frontend/src/components/TagDetailSidebar.tsx b/frontend/src/components/TagDetailSidebar.tsx
index be95412..24dae59 100644
--- a/frontend/src/components/TagDetailSidebar.tsx
+++ b/frontend/src/components/TagDetailSidebar.tsx
@@ -26,13 +26,13 @@ import { dateString, originalCreatedAtString } from '@/lib/utils'
 import type { DragEndEvent } from '@dnd-kit/core'
 import type { FC, MutableRefObject, ReactNode } from 'react'
 
-import type { Category, Post, Tag } from '@/types'
+import type { Category, Post, TagWithSections } from '@/types'
 
-type TagByCategory = { [key in Category]: Tag[] }
+type TagByCategory = { [key in Category]: TagWithSections[] }
 
 
 const renderTagTree = (
-    tag:              Tag,
+    tag:              TagWithSections,
     nestLevel:        number,
     path:             string,
     suppressClickRef: MutableRefObject<boolean>,
@@ -63,7 +63,7 @@ const renderTagTree = (
 
 
 const isDescendant = (
-    root:     Tag,
+    root:     TagWithSections,
     targetId: number,
 ): boolean => {
   if (!(root.children))
@@ -84,8 +84,8 @@ const isDescendant = (
 const findTag = (
     byCat:  TagByCategory,
     id:     number,
-): Tag | undefined => {
-  const walk = (nodes: Tag[]): Tag | undefined => {
+): TagWithSections | undefined => {
+  const walk = (nodes: TagWithSections[]): TagWithSections | undefined => {
     for (const t of nodes)
       {
 	if (t.id === id)
@@ -167,7 +167,7 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
       }
 
     for (const cat of Object.keys (tagsTmp) as (keyof typeof tagsTmp)[])
-      tagsTmp[cat].sort ((tagA: Tag, tagB: Tag) => tagA.name < tagB.name ? -1 : 1)
+      tagsTmp[cat].sort ((tagA: TagWithSections, tagB: TagWithSections) => tagA.name < tagB.name ? -1 : 1)
 
     return tagsTmp
   }, [post])
@@ -378,4 +378,4 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
       </SidebarComponent>)
 }
 
-export default TagDetailSidebar
\ No newline at end of file
+export default TagDetailSidebar
diff --git a/frontend/src/lib/utils.ts b/frontend/src/lib/utils.ts
index 672ebd2..6493039 100644
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@@ -77,7 +77,7 @@ export const msToTime = (ms: number): string => {
   const totalS = Math.trunc (ms / 1_000)
   const s = String (totalS % 60)
   const min = String (Math.trunc (totalS / 60) % 60)
-  const h = String (Math.trunc (totalS / 3_600))
+  const h = Math.trunc (totalS / 3_600)
 
   return (h > 0
 	  ? `${ h }:${ min.padStart (2, '0') }:${ s.padStart (2, '0') }`
diff --git a/frontend/src/pages/tags/TagDetailPage.tsx b/frontend/src/pages/tags/TagDetailPage.tsx
index fc10727..7d6eb57 100644
--- a/frontend/src/pages/tags/TagDetailPage.tsx
+++ b/frontend/src/pages/tags/TagDetailPage.tsx
@@ -157,4 +157,4 @@ const TagDetailPage: FC = () => {
       </MainArea>)
 }
 
-export default TagDetailPage
\ No newline at end of file
+export default TagDetailPage
diff --git a/frontend/src/test/factories.ts b/frontend/src/test/factories.ts
index 2092619..929f4f1 100644
--- a/frontend/src/test/factories.ts
+++ b/frontend/src/test/factories.ts
@@ -1,6 +1,6 @@
-import type { Material, Post, Tag, User, WikiPage } from '@/types'
+import type { Material, Post, TagWithSections, User, WikiPage } from '@/types'
 
-export const buildTag = (overrides: Partial<Tag> = {}): Tag => ({
+export const buildTag = (overrides: Partial<TagWithSections> = {}): TagWithSections => ({
   id:             1,
   name:           'テストタグ',
   category:       'general',
@@ -13,6 +13,8 @@ export const buildTag = (overrides: Partial<Tag> = {}): Tag => ({
   materialId:     null,
   hasDeerjikists: false,
   matchedAlias:   null,
+  sections:       [],
+  children:       [],
   ...overrides,
 })
 
-- 
2.34.1


From 7e89fb286abbc2eff84e7c3c4e5edab471363369 Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Sat, 23 May 2026 07:21:15 +0900
Subject: [PATCH 3/7] #351

---
 backend/app/models/tag.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index f65ce24..1d19df5 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -120,7 +120,7 @@ class Tag < ApplicationRecord
 
       find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         tag.update!(category: cat) if cat && tag.category != cat
-        next if sections_by_tag.blank?
+        next if sections_by_tag.empty?
 
         sections[tag.id] ||= []
         sections[tag.id].concat(sections_by_tag)
-- 
2.34.1


From d3af4563ca5995056971dab3315ecc019c7a0c86 Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Mon, 22 Jun 2026 21:24:55 +0900
Subject: [PATCH 4/7] #351

---
 backend/app/controllers/posts_controller.rb   |  30 +++--
 backend/app/models/post.rb                    |   2 +-
 backend/app/models/post_tag_section.rb        |   4 +-
 backend/app/models/tag.rb                     | 103 ++++++++++++++----
 backend/app/representations/post_repr.rb      |  14 ++-
 ...0260622010000_create_post_tag_sections.rb} |   4 +-
 backend/db/schema.rb                          |   7 +-
 backend/spec/models/post_tag_spec.rb          |  12 ++
 backend/spec/models/tag_spec.rb               |  79 ++++++++++++++
 backend/spec/requests/posts_spec.rb           |  97 +++++++++++++++++
 frontend/src/components/PostEditForm.tsx      |   2 +-
 frontend/src/types.ts                         |   2 +-
 12 files changed, 309 insertions(+), 47 deletions(-)
 rename backend/db/migrate/{20260518235300_create_post_tag_sections.rb => 20260622010000_create_post_tag_sections.rb} (86%)

diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 068795a..941d7aa 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -45,7 +45,9 @@ class PostsController < ApplicationController
         .joins("LEFT JOIN (#{ pt_max_sql }) pt_max ON pt_max.post_id = posts.id")
         .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
         .preload(:uploaded_user, :parents, :children,
-                 tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                 active_post_tags: [:sections,
+                                    { tag: [:deerjikists, :materials,
+                                            { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -97,7 +99,9 @@ class PostsController < ApplicationController
 
   def random
     post = filtered_posts.preload(:uploaded_user, :parents, :children,
-                                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                                  active_post_tags: [:sections,
+                                                     { tag: [:deerjikists, :materials,
+                                                             { tag_name: :wiki_page }] }])
                          .with_attached_thumbnail
                          .order('RAND()')
                          .first
@@ -110,7 +114,9 @@ class PostsController < ApplicationController
     post =
         Post
         .includes(:uploaded_user, :parents, :children,
-                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                  active_post_tags: [:sections,
+                                     { tag: [:deerjikists, :materials,
+                                             { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
         .find_by(id: params[:id])
     return head :not_found unless post
@@ -168,6 +174,8 @@ class PostsController < ApplicationController
     render_validation_error fields: { tags: 'ニコニコ・タグは直接指定できません．' }
   rescue Tag::DeprecatedTagNormalisationError
     render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
+  rescue Tag::SectionLiteralParseError
+    render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
   rescue ArgumentError => e
     render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
@@ -260,6 +268,8 @@ class PostsController < ApplicationController
     render_validation_error fields: { tags: ['ニコニコ・タグは直接指定できません．'] }
   rescue Tag::DeprecatedTagNormalisationError
     render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
+  rescue Tag::SectionLiteralParseError
+    render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
   rescue ArgumentError => e
     render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
@@ -390,7 +400,8 @@ class PostsController < ApplicationController
   end
 
   def build_tag_tree_for post
-    tags = post.tags.reject(&:deprecated?).to_a
+    post_tags = post.active_post_tags.reject { |post_tag| post_tag.tag.deprecated? }
+    tags = post_tags.map(&:tag)
     tag_ids = tags.map(&:id)
 
     implications = TagImplication.where(parent_tag_id: tag_ids, tag_id: tag_ids)
@@ -405,11 +416,9 @@ class PostsController < ApplicationController
     root_ids = tag_ids - child_ids
 
     tags_by_id = tags.index_by(&:id)
-    sections_by_tag_id =
-        PostTagSection
-        .where(post_id: post.id, tag_id: tag_ids)
-        .order(:begin_ms)
-        .group_by(&:tag_id)
+    sections_by_tag_id = post_tags.to_h { |post_tag|
+      [post_tag.tag_id, post_tag.sections.as_json(only: [:begin_ms, :end_ms])]
+    }
 
     memo = { }
 
@@ -418,7 +427,6 @@ class PostsController < ApplicationController
       return nil unless tag
 
       sections = sections_by_tag_id.fetch(tag_id, [])
-                                   .as_json(only: [:begin_ms, :end_ms])
 
       if path.include?(tag_id)
         return TagRepr.inline(tag).merge(children: [], sections:)
@@ -578,7 +586,7 @@ class PostsController < ApplicationController
   end
 
   def section_literal section
-    "[#{ Post.ms_to_time(section[0]) }-#{ Post.ms_to_time(section[1]) }]"
+    "[#{ Post.ms_to_time(section[0]) }-#{ section[1] ? Post.ms_to_time(section[1]) : '' }]"
   end
 
   def post_conflict_json post:, base_version_no:, base_snapshot:,
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 0342c7f..913f1d4 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -86,7 +86,7 @@ class Post < ApplicationRecord
   end
 
   def self.section_literal section
-    "[#{ Post.ms_to_time(section.begin_ms) }-#{ Post.ms_to_time(section.end_ms) }]"
+    "[#{ Post.ms_to_time(section.begin_ms) }-#{ section.end_ms ? Post.ms_to_time(section.end_ms) : '' }]"
   end
 
   def self.ms_to_time ms
diff --git a/backend/app/models/post_tag_section.rb b/backend/app/models/post_tag_section.rb
index 8d6af9e..5c47e4c 100644
--- a/backend/app/models/post_tag_section.rb
+++ b/backend/app/models/post_tag_section.rb
@@ -15,6 +15,6 @@ class PostTagSection < ApplicationRecord
   validates :begin_ms, presence: true,
                        numericality: { only_integer: true, greater_than_or_equal_to: 0 }
 
-  validates :end_ms, presence: true,
-                     numericality: { only_integer: true, greater_than: :begin_ms }
+  validates :end_ms, numericality: { only_integer: true, greater_than: :begin_ms },
+                     allow_nil: true
 end
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 7cd6a48..6e87f44 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -17,6 +17,16 @@ class Tag < ApplicationRecord
     end
   end
 
+  class SectionLiteralParseError < ArgumentError
+    attr_reader :tag_name, :literal
+
+    def initialize tag_name, literal
+      @tag_name = tag_name
+      @literal = literal
+      super("invalid section literal for tag #{ tag_name }: #{ literal }")
+    end
+  end
+
   has_many :post_tags, inverse_of: :tag
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
@@ -113,20 +123,22 @@ class Tag < ApplicationRecord
 
     sections = { }
     tags = tag_names.map do |name|
+      raw_name = name
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
 
       name = name.sub(/\A#{ pf }/i, '')
 
       sections_by_tag = []
-      while n = name.sub!(/^(\S*?)\[([0-9:.]*?)-([0-9:.]*?)\](\S*?)$/, '\1\4 \2 \3')
-        name, *section_raw = n.split
+      while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
+        name = "#{ match[1] }#{ match[4] }"
+        sections_by_tag << normalise_section_range!(
+            begin_raw: match[2],
+            end_raw: match[3],
+            tag_name: name)
+      end
 
-        begin_ms, end_ms = section_raw.map { time_to_ms(_1) }
-        next if begin_ms == end_ms
-
-        begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
-
-        sections_by_tag << [begin_ms, end_ms]
+      if name.include?('[') || name.include?(']')
+        raise SectionLiteralParseError.new(raw_name, raw_name)
       end
 
       name = TagName.canonicalise(name).first
@@ -141,6 +153,7 @@ class Tag < ApplicationRecord
 
         sections[tag.id] ||= []
         sections[tag.id].concat(sections_by_tag)
+        sections[tag.id] = merge_section_ranges(sections[tag.id])
       end
     end
 
@@ -178,6 +191,45 @@ class Tag < ApplicationRecord
     (result + tags).uniq { |t| t.id }
   end
 
+  def self.normalise_section_range! begin_raw:, end_raw:, tag_name:
+    begin_ms = begin_raw.empty? ? 0 : time_to_ms!(begin_raw, tag_name:)
+    end_ms = end_raw.empty? ? nil : time_to_ms!(end_raw, tag_name:)
+
+    if end_ms
+      begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
+      end_ms = begin_ms + 1 if begin_ms == end_ms
+    end
+
+    [begin_ms, end_ms]
+  end
+
+  def self.merge_section_ranges ranges
+    sorted_ranges = ranges.sort_by { |begin_ms, end_ms| [begin_ms, end_ms || Float::INFINITY] }
+    merged = []
+
+    sorted_ranges.each do |begin_ms, end_ms|
+      if merged.empty?
+        merged << [begin_ms, end_ms]
+        next
+      end
+
+      last_begin_ms, last_end_ms = merged[-1]
+      if last_end_ms.nil? || begin_ms <= last_end_ms
+        merged[-1] = [last_begin_ms, merge_section_end(last_end_ms, end_ms)]
+      else
+        merged << [begin_ms, end_ms]
+      end
+    end
+
+    merged
+  end
+
+  def self.merge_section_end left_end_ms, right_end_ms
+    return nil if left_end_ms.nil? || right_end_ms.nil?
+
+    [left_end_ms, right_end_ms].max
+  end
+
   def self.find_or_create_by_tag_name! name, category:
     tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
     tn = tn.canonical if tn.canonical_id?
@@ -274,23 +326,30 @@ class Tag < ApplicationRecord
     end
   end
 
-  def self.time_to_ms str
-    parts = str.split(':')
+  def self.time_to_ms! str, tag_name:
+    match =
+        case str
+        when /\A(?<seconds>\d+)(?:\.(?<ms>\d{1,3}))?\z/
+          { hours: nil, minutes: nil, seconds: Regexp.last_match[:seconds],
+            ms: Regexp.last_match[:ms] }
+        when /\A(?<minutes>\d+):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
+          { hours: nil, minutes: Regexp.last_match[:minutes],
+            seconds: Regexp.last_match[:seconds],
+            ms: Regexp.last_match[:ms] }
+        when /\A(?<hours>\d+):(?<minutes>[0-5]?\d):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
+          { hours: Regexp.last_match[:hours],
+            minutes: Regexp.last_match[:minutes],
+            seconds: Regexp.last_match[:seconds],
+            ms: Regexp.last_match[:ms] }
+        end
 
-    s_part = parts.pop
-    s, ms = s_part.split('.')
+    raise SectionLiteralParseError.new(tag_name, str) unless match
 
-    total_s = s.to_i
+    total_s = match[:seconds].to_i
+    total_s += match[:minutes].to_i * 60 if match[:minutes]
+    total_s += match[:hours].to_i * 3_600 if match[:hours]
 
-    if parts.length >= 1
-      total_s += parts.pop.to_i * 60
-    end
-
-    if parts.length >= 1
-      total_s += parts.pop.to_i * 3_600
-    end
-
-    total_s * 1_000 + ms.to_s.ljust(3, '0')[0, 3].to_i
+    total_s * 1_000 + match[:ms].to_s.ljust(3, '0')[0, 3].to_i
   end
 
   def nico_tags_cannot_be_deprecated
diff --git a/backend/app/representations/post_repr.rb b/backend/app/representations/post_repr.rb
index 1c62f1e..8fe6f58 100644
--- a/backend/app/representations/post_repr.rb
+++ b/backend/app/representations/post_repr.rb
@@ -18,7 +18,7 @@ module PostRepr
 
   def base post, current_user = nil
     json = common(post)
-    json['tags'] = tag_json(post.tags)
+    json['tags'] = tag_json(post)
     json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
     json['viewed'] = current_user ? current_user.viewed?(post) : false
     json
@@ -52,8 +52,16 @@ module PostRepr
                .merge('thumbnail' => thumbnail_url(post))
   end
 
-  def tag_json tags
-    tags.reject(&:deprecated?).map { |tag| TagRepr.inline(tag) }
+  def tag_json post
+    post
+        .active_post_tags
+        .reject { _1.tag.deprecated? }
+        .sort_by { _1.tag.name }
+        .map { |post_tag|
+      TagRepr.inline(post_tag.tag).merge(
+          'children' => [],
+          'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
+    }
   end
 
   def thumbnail_url post
diff --git a/backend/db/migrate/20260518235300_create_post_tag_sections.rb b/backend/db/migrate/20260622010000_create_post_tag_sections.rb
similarity index 86%
rename from backend/db/migrate/20260518235300_create_post_tag_sections.rb
rename to backend/db/migrate/20260622010000_create_post_tag_sections.rb
index ff87e20..042d05b 100644
--- a/backend/db/migrate/20260518235300_create_post_tag_sections.rb
+++ b/backend/db/migrate/20260622010000_create_post_tag_sections.rb
@@ -4,7 +4,7 @@ class CreatePostTagSections < ActiveRecord::Migration[8.0]
       t.references :post, null: false, foreign_key: true, index: false
       t.references :tag, null: false, foreign_key: true, index: false
       t.integer :begin_ms, null: false
-      t.integer :end_ms, null: false
+      t.integer :end_ms, null: true
       t.timestamps
 
       t.index [:post_id, :begin_ms], name: 'idx_post_tag_sections_post_id_begin_ms'
@@ -12,7 +12,7 @@ class CreatePostTagSections < ActiveRecord::Migration[8.0]
       t.check_constraint 'begin_ms >= 0',
                          name: 'chk_post_tag_sections_begin_ms_natural'
 
-      t.check_constraint 'begin_ms < end_ms',
+      t.check_constraint 'end_ms IS NULL OR begin_ms < end_ms',
                          name: 'chk_post_tag_sections_end_ms_after_begin_ms'
     end
   end
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index 62f6808..2cc6a9a 100644
--- a/backend/db/schema.rb
+++ b/backend/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_06_21_000000) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_22_010000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -214,12 +214,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_21_000000) do
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
     t.integer "begin_ms", null: false
-    t.integer "end_ms", null: false
+    t.integer "end_ms"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["post_id", "begin_ms"], name: "idx_post_tag_sections_post_id_begin_ms"
     t.index ["tag_id"], name: "fk_rails_8be3847903"
-    t.check_constraint "`begin_ms` < `end_ms`", name: "chk_post_tag_sections_end_ms_after_begin_ms"
+    t.check_constraint "(`end_ms` is null) or (`begin_ms` < `end_ms`)", name: "chk_post_tag_sections_end_ms_after_begin_ms"
     t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
   end
 
@@ -432,7 +432,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_21_000000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["expires_at"], name: "index_theatre_watching_users_on_expires_at"
-    t.index ["theatre_id", "expires_at"], name: "idx_on_theatre_id_skip_expires_at_4c8de1dd42"
     t.index ["theatre_id", "expires_at"], name: "index_theatre_watching_users_on_theatre_id_and_expires_at"
     t.index ["theatre_id"], name: "index_theatre_watching_users_on_theatre_id"
     t.index ["user_id"], name: "index_theatre_watching_users_on_user_id"
diff --git a/backend/spec/models/post_tag_spec.rb b/backend/spec/models/post_tag_spec.rb
index 551f3fd..6f89ac5 100644
--- a/backend/spec/models/post_tag_spec.rb
+++ b/backend/spec/models/post_tag_spec.rb
@@ -25,5 +25,17 @@ RSpec.describe PostTag, type: :model do
 
       expect(post_tag.sections).to be_empty
     end
+
+    it 'allows open-ended sections' do
+      post_tag = create(:post_tag)
+      section = create(:post_tag_section,
+                       post: post_tag.post,
+                       tag: post_tag.tag,
+                       begin_ms: 1000,
+                       end_ms: nil)
+
+      expect(section).to be_valid
+      expect(post_tag.sections).to contain_exactly(section)
+    end
   end
 end
diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index 014cdde..5899acb 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -19,6 +19,85 @@ RSpec.describe Tag, type: :model do
         expect(error.tag_names).to eq([deprecated_tag.name])
       }
     end
+
+    it 'rejects invalid section literals instead of treating them as zero' do
+      expect {
+        described_class.normalise_tags!(
+          ['normalise_invalid_section[1:aa-2:00]'],
+          with_sections: true
+        )
+      }.to raise_error(Tag::SectionLiteralParseError)
+    end
+
+    it 'parses open-ended section literals' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
+    end
+
+    it 'parses omitted begin as zero' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[-1:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, 60_000]])
+    end
+
+    it 'parses fully open section literals as zero to end-of-video' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[-]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, nil]])
+    end
+
+    it 'expands zero-width sections to one millisecond' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-1:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 60_001]])
+    end
+
+    it 'swaps reversed section boundaries' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[2:00-1:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 120_000]])
+    end
+
+    it 'merges open-ended sections over later bounded sections' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-][2:00-3:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
+    end
+
+    it 'merges adjacent bounded and open-ended sections' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-3:00][3:00-]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
+    end
   end
 
   describe '.expand_parent_tags' do
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 18d5b73..7381615 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -127,6 +127,22 @@ RSpec.describe 'Posts API', type: :request do
       expect(all_tag_names).to include("spec_tag")
     end
 
+    it 'keeps children and sections keys in non-detail tag responses' do
+      PostTagSection.create!(post: hit_post, tag:, begin_ms: 1_000, end_ms: nil)
+
+      get '/posts'
+
+      expect(response).to have_http_status(:ok)
+
+      hit_json = json.fetch('posts').find { |post| post['id'] == hit_post.id }
+      tag_json = hit_json.fetch('tags').find { |item| item['name'] == 'spec_tag' }
+
+      expect(tag_json.fetch('children')).to eq([])
+      expect(tag_json.fetch('sections')).to eq([
+        { 'begin_ms' => 1_000, 'end_ms' => nil }
+      ])
+    end
+
     context "when q is provided" do
       it "filters posts by q (hit case)" do
         get "/posts", params: { tags: "spec_tag" }
@@ -767,6 +783,87 @@ RSpec.describe 'Posts API', type: :request do
       expect(saved_names).not_to include('deprecated_parent', 'deprecated_grandparent')
     end
 
+    it 'returns validation error for an invalid section literal' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'invalid section literal',
+        url: 'https://example.com/invalid-section-literal',
+        tags: 'spec_tag[1:aa-2:00]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json).to include(
+        'type' => 'validation_error',
+        'message' => '入力内容を確認してください．'
+      )
+      expect(json.fetch('errors')).to include(
+        'tags' => ['タグ区間の記法が不正です．']
+      )
+    end
+
+    it 'saves open-ended sections with end_ms NULL' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'open ended section literal',
+        url: 'https://example.com/open-ended-section-literal',
+        tags: '伊地知ニジカ[1:00-]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+
+      created_post = Post.find(json.fetch('id'))
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      section = PostTagSection.find_by!(post: created_post, tag:)
+
+      expect(section.begin_ms).to eq(60_000)
+      expect(section.end_ms).to be_nil
+    end
+
+    it 'treats [-] as [0:00-] and saves end_ms NULL' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'fully open section literal',
+        url: 'https://example.com/fully-open-section-literal',
+        tags: '伊地知ニジカ[-]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+
+      created_post = Post.find(json.fetch('id'))
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      section = PostTagSection.find_by!(post: created_post, tag:)
+
+      expect(section.begin_ms).to eq(0)
+      expect(section.end_ms).to be_nil
+    end
+
+    it 'returns end_ms null for open-ended sections in show response' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'show open ended section literal',
+        url: 'https://example.com/show-open-ended-section-literal',
+        tags: '伊地知ニジカ[1:00-]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+
+      get "/posts/#{ json.fetch('id') }"
+
+      expect(response).to have_http_status(:ok)
+      tag_json = json.fetch('tags').find { |item| item['name'] == '伊地知ニジカ' }
+      expect(tag_json.fetch('sections')).to eq([
+        { 'begin_ms' => 60_000, 'end_ms' => nil }
+      ])
+    end
+
     context "when nico tag already exists in tags" do
       before do
         Tag.find_undiscard_or_create_by!(
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 6e4b560..1ed75bd 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -33,7 +33,7 @@ const tagsToStr = (tags: TagWithSections[]): string => {
 
   return [...(new Set (result.map (t =>
       `${ t.name }${ t.sections
-		     .map (s => `[${ msToTime (s.beginMs) }-${ msToTime (s.endMs) }]`)
+		     .map (s => `[${ msToTime (s.beginMs) }-${ s.endMs == null ? '' : msToTime (s.endMs) }]`)
 		     .join ('') }`)))].join (' ')
 }
 
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index 641af6c..6b37dc0 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -221,7 +221,7 @@ export type TagVersion = {
     createdByUser:          { id: number; name: string | null } | null }
 
 export type TagWithSections = Tag & { sections: { beginMs:  number
-						  endMs:    number }[]
+						  endMs:    number | null }[]
 			              children: TagWithSections[] }
 
 export type Theatre = {
-- 
2.34.1


From 53d1cadefb7080310bcdf8784ab6626cbbbb5abe Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Tue, 23 Jun 2026 00:24:04 +0900
Subject: [PATCH 5/7] #351

---
 .../controllers/post_versions_controller.rb   |   5 +
 backend/app/controllers/posts_controller.rb   |  88 +++++++++++---
 backend/app/models/post.rb                    |  15 ++-
 backend/app/models/post_version.rb            |   1 +
 backend/app/models/tag.rb                     |   3 +
 backend/app/representations/post_repr.rb      |   1 +
 backend/app/services/post_version_recorder.rb |   1 +
 ...622020000_add_video_ms_to_post_versions.rb |   9 ++
 backend/db/schema.rb                          |   5 +-
 backend/spec/models/tag_spec.rb               |  14 ++-
 backend/spec/requests/posts_spec.rb           | 108 +++++++++++++++++-
 frontend/src/components/PostEditForm.tsx      |  39 ++++++-
 frontend/src/lib/posts.ts                     |   2 +
 frontend/src/lib/utils.test.ts                |  13 ++-
 frontend/src/lib/utils.ts                     |  10 +-
 frontend/src/pages/posts/PostHistoryPage.tsx  |   8 +-
 frontend/src/pages/posts/PostNewPage.tsx      |  29 ++++-
 frontend/src/test/factories.ts                |   1 +
 frontend/src/types.ts                         |   2 +
 19 files changed, 316 insertions(+), 38 deletions(-)
 create mode 100644 backend/db/migrate/20260622020000_add_video_ms_to_post_versions.rb

diff --git a/backend/app/controllers/post_versions_controller.rb b/backend/app/controllers/post_versions_controller.rb
index 04032e3..ae3d897 100644
--- a/backend/app/controllers/post_versions_controller.rb
+++ b/backend/app/controllers/post_versions_controller.rb
@@ -25,6 +25,7 @@ class PostVersionsController < ApplicationController
         SQL
         .select('post_versions.*', 'prev.title AS prev_title', 'prev.url AS prev_url',
                 'prev.thumbnail_base AS prev_thumbnail_base', 'prev.tags AS prev_tags',
+                'prev.video_ms AS prev_video_ms',
                 'prev.original_created_from AS prev_original_created_from',
                 'prev.original_created_before AS prev_original_created_before')
     q = q.where('post_versions.post_id = ?', post_id) if post_id
@@ -74,6 +75,10 @@ class PostVersionsController < ApplicationController
           current: row.thumbnail_base,
           prev: row.attributes['prev_thumbnail_base']
         },
+        video_ms: {
+          current: row.video_ms,
+          prev: row.attributes['prev_video_ms']
+        },
         tags: build_version_tags(cur_tags, prev_tags),
         original_created_from: {
           current: row.original_created_from&.iso8601,
diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 941d7aa..73f3d1c 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -1,6 +1,10 @@
 class PostsController < ApplicationController
   Event = Struct.new(:post, :tag, :user, :change_type, :timestamp, keyword_init: true)
 
+  class VideoMsParseError < ArgumentError
+    ;
+  end
+
   def index
     url = params[:url].presence
     title = params[:title].presence
@@ -159,6 +163,9 @@ class PostsController < ApplicationController
       TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
 
       tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
+      post.video_ms = normalise_video_ms(tags)
+      validate_video_sections!(post.video_ms, sections)
+      post.save!
       sync_post_tags!(post, tags, sections)
 
       sync_parent_posts!(post, parent_post_ids)
@@ -176,6 +183,8 @@ class PostsController < ApplicationController
     render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
   rescue Tag::SectionLiteralParseError
     render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
+  rescue VideoMsParseError
+    render_validation_error fields: { video_ms: ['動画時間の記法が不正です．'] }
   rescue ArgumentError => e
     render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
@@ -232,6 +241,8 @@ class PostsController < ApplicationController
                                                  original_created_from:,
                                                  original_created_before:,
                                                  tag_names:,
+                                                 video_ms_param: params[:video_ms],
+                                                 duration_param: params[:duration],
                                                  parent_post_ids:)
 
       snapshot_to_apply =
@@ -270,6 +281,8 @@ class PostsController < ApplicationController
     render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
   rescue Tag::SectionLiteralParseError
     render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
+  rescue VideoMsParseError
+    render_validation_error fields: { video_ms: ['動画時間の記法が不正です．'] }
   rescue ArgumentError => e
     render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
@@ -510,6 +523,7 @@ class PostsController < ApplicationController
 
   def post_snapshot_from_version version
     { title: version.title,
+      video_ms: version.respond_to?(:video_ms) ? version.video_ms : nil,
       original_created_from: snapshot_time(version.original_created_from),
       original_created_before: snapshot_time(version.original_created_before),
       tag_names: editable_tag_names_from_version(version),
@@ -522,6 +536,7 @@ class PostsController < ApplicationController
 
   def post_snapshot_from_record post
     { title: post.title,
+      video_ms: post.video_ms,
       original_created_from: snapshot_time(post.original_created_from),
       original_created_before: snapshot_time(post.original_created_before),
       tag_names: editable_tag_names_from_post(post),
@@ -548,11 +563,22 @@ class PostsController < ApplicationController
   end
 
   def post_incoming_snapshot title:, original_created_from:, original_created_before:,
-                             tag_names:, parent_post_ids:
+                             tag_names:, video_ms_param:, duration_param:, parent_post_ids:
+    Tag.normalise_tags!(tag_names, with_tagme: false, deny_deprecated: true,
+                                        with_sections: true) =>
+        { tags:, sections: }
+
+    tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
+    video_ms = normalise_video_ms(tags, video_ms_param:, duration_param:)
+    validate_video_sections!(video_ms, sections)
+
     { title:,
+      video_ms:,
       original_created_from: snapshot_time(original_created_from),
       original_created_before: snapshot_time(original_created_before),
-      tag_names: incoming_tag_names_for_snapshot(tag_names),
+      tag_names: tags.uniq(&:id).map { |tag|
+        "#{ tag.name }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
+      }.sort,
       parent_post_ids: parent_post_ids.sort }
   end
 
@@ -575,16 +601,6 @@ class PostsController < ApplicationController
     value.to_s
   end
 
-  def incoming_tag_names_for_snapshot raw_tag_names
-    Tag.normalise_tags!(raw_tag_names, with_tagme: false, deny_deprecated: true,
-                                        with_sections: true) =>
-        { tags:, sections: }
-
-    Tag.expand_parent_tags(tags).reject(&:deprecated?).uniq(&:id).map { |tag|
-      "#{ tag.name }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
-    }.sort
-  end
-
   def section_literal section
     "[#{ Post.ms_to_time(section[0]) }-#{ section[1] ? Post.ms_to_time(section[1]) : '' }]"
   end
@@ -607,6 +623,8 @@ class PostsController < ApplicationController
   def post_snapshot_changes base_snapshot, current_snapshot, incoming_snapshot
     [scalar_snapshot_change(:title, 'タイトル',
                             base_snapshot, current_snapshot, incoming_snapshot),
+     scalar_snapshot_change(:video_ms, '動画時間',
+                            base_snapshot, current_snapshot, incoming_snapshot),
      scalar_snapshot_change(:original_created_from, 'オリジナルの作成日時（以降）',
                             base_snapshot, current_snapshot, incoming_snapshot),
      scalar_snapshot_change(:original_created_before, 'オリジナルの作成日時（より前）',
@@ -670,6 +688,7 @@ class PostsController < ApplicationController
     PostVersionRecorder.ensure_snapshot!(post, created_by_user: current_user)
 
     post.update!(title: snapshot[:title],
+                 video_ms: snapshot[:video_ms],
                  original_created_from: snapshot[:original_created_from],
                  original_created_before: snapshot[:original_created_before])
 
@@ -684,6 +703,9 @@ class PostsController < ApplicationController
     tags = readonly_tags + editable_tags
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
 
+    post.video_ms = tags.any? { _1.id == Tag.video.id } ? snapshot[:video_ms] : nil
+    validate_video_sections!(post.video_ms, sections)
+    post.save!
     sync_post_tags!(post, tags, sections)
     sync_parent_posts!(post, snapshot[:parent_post_ids])
 
@@ -691,7 +713,7 @@ class PostsController < ApplicationController
   end
 
   def merge_post_snapshots base_snapshot, current_snapshot, incoming_snapshot
-    [:title, :original_created_from, :original_created_before].map {
+    [:title, :video_ms, :original_created_from, :original_created_before].map {
       [_1, merge_scalar_snapshot_value(base_snapshot[_1],
                                        current_snapshot[_1],
                                        incoming_snapshot[_1])]
@@ -735,4 +757,44 @@ class PostsController < ApplicationController
       render_validation_error record
     end
   end
+
+  def normalise_video_ms tags, video_ms_param: params[:video_ms], duration_param: params[:duration]
+    return nil unless tags.any? { _1.id == Tag.video.id }
+
+    if video_ms_param.present?
+      video_ms = Integer(video_ms_param, exception: false)
+      raise VideoMsParseError unless video_ms&.positive?
+
+      return video_ms
+    end
+
+    return nil if duration_param.blank?
+
+    video_ms = Tag.time_to_ms!(duration_param.to_s, tag_name: '動画時間')
+    raise VideoMsParseError unless video_ms.positive?
+
+    video_ms
+  rescue Tag::SectionLiteralParseError
+    raise VideoMsParseError
+  end
+
+  def validate_video_sections! video_ms, sections
+    return unless video_ms
+
+    sections.each_value do |ranges|
+      ranges.each do |begin_ms, end_ms|
+        if begin_ms >= video_ms
+          post = Post.new
+          post.errors.add :video_ms, 'タグ区間の開始が動画時間以上です．'
+          raise ActiveRecord::RecordInvalid, post
+        end
+
+        if end_ms && end_ms > video_ms
+          post = Post.new
+          post.errors.add :video_ms, 'タグ区間の終端が動画時間を超えてゐます．'
+          raise ActiveRecord::RecordInvalid, post
+        end
+      end
+    end
+  end
 end
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 913f1d4..633d3b4 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -46,6 +46,7 @@ class Post < ApplicationRecord
   before_validation :normalise_url
 
   validates :url, presence: true, uniqueness: true
+  validates :video_ms, numericality: { only_integer: true, greater_than: 0 }, allow_nil: true
 
   validate :validate_original_created_range
   validate :url_must_be_http_url
@@ -94,12 +95,16 @@ class Post < ApplicationRecord
     s = total_s % 60
     min = (total_s / 60) % 60
     h = total_s / 3_600
+    remainder_ms = ms % 1_000
 
-    if h.positive?
-      '%d:%02d:%02d' % [h, min, s]
-    else
-      '%d:%02d' % [min, s]
-    end
+    base =
+        if h.positive?
+          '%d:%02d:%02d' % [h, min, s]
+        else
+          '%d:%02d' % [min, s]
+        end
+
+    remainder_ms.positive? ? "#{ base }.#{ remainder_ms.to_s.rjust(3, '0') }" : base
   end
 
   def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
diff --git a/backend/app/models/post_version.rb b/backend/app/models/post_version.rb
index 523d1a0..8fe52bb 100644
--- a/backend/app/models/post_version.rb
+++ b/backend/app/models/post_version.rb
@@ -5,6 +5,7 @@ class PostVersion < ApplicationRecord
   belongs_to :parent, class_name: 'Post', optional: true
 
   validates :url, presence: true
+  validates :video_ms, numericality: { only_integer: true, greater_than: 0 }, allow_nil: true
 
   validate :validate_original_created_range
 
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 6e87f44..202610b 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -131,6 +131,8 @@ class Tag < ApplicationRecord
       sections_by_tag = []
       while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
         name = "#{ match[1] }#{ match[4] }"
+        next if match[2].empty? && match[3].empty?
+
         sections_by_tag << normalise_section_range!(
             begin_raw: match[2],
             end_raw: match[3],
@@ -154,6 +156,7 @@ class Tag < ApplicationRecord
         sections[tag.id] ||= []
         sections[tag.id].concat(sections_by_tag)
         sections[tag.id] = merge_section_ranges(sections[tag.id])
+        sections.delete(tag.id) if sections[tag.id] == [[0, nil]]
       end
     end
 
diff --git a/backend/app/representations/post_repr.rb b/backend/app/representations/post_repr.rb
index 8fe6f58..c878291 100644
--- a/backend/app/representations/post_repr.rb
+++ b/backend/app/representations/post_repr.rb
@@ -8,6 +8,7 @@ module PostRepr
       :url,
       :title,
       :thumbnail_base,
+      :video_ms,
       :original_created_from,
       :original_created_before,
       :created_at,
diff --git a/backend/app/services/post_version_recorder.rb b/backend/app/services/post_version_recorder.rb
index 9e3fd15..0726884 100644
--- a/backend/app/services/post_version_recorder.rb
+++ b/backend/app/services/post_version_recorder.rb
@@ -23,6 +23,7 @@ class PostVersionRecorder < VersionRecorder
     { title: @record.title,
       url: @record.url,
       thumbnail_base: @record.thumbnail_base,
+      video_ms: @record.video_ms,
       tags: @record.snapshot_tag_names.join(' '),
       parent_post_ids: @record.snapshot_parent_post_ids.join(' '),
       original_created_from: @record.original_created_from,
diff --git a/backend/db/migrate/20260622020000_add_video_ms_to_post_versions.rb b/backend/db/migrate/20260622020000_add_video_ms_to_post_versions.rb
new file mode 100644
index 0000000..9741213
--- /dev/null
+++ b/backend/db/migrate/20260622020000_add_video_ms_to_post_versions.rb
@@ -0,0 +1,9 @@
+class AddVideoMsToPostVersions < ActiveRecord::Migration[8.0]
+  def change
+    add_column :post_versions, :video_ms, :integer
+    add_index :post_versions, [:video_ms, :post_id], name: 'idx_post_versions_video_ms_post_id'
+
+    add_check_constraint :post_versions, 'video_ms IS NULL OR video_ms > 0',
+                         name: 'chk_post_versions_video_ms_positive'
+  end
+end
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index 2cc6a9a..d8c15cf 100644
--- a/backend/db/schema.rb
+++ b/backend/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_06_22_010000) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_22_020000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -256,9 +256,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_22_010000) do
     t.datetime "original_created_before"
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
+    t.integer "video_ms"
     t.index ["created_by_user_id"], name: "index_post_versions_on_created_by_user_id"
     t.index ["post_id", "version_no"], name: "index_post_versions_on_post_id_and_version_no", unique: true
     t.index ["post_id"], name: "index_post_versions_on_post_id"
+    t.index ["video_ms", "post_id"], name: "idx_post_versions_video_ms_post_id"
+    t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_post_versions_video_ms_positive"
     t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
     t.check_constraint "`version_no` > 0", name: "post_versions_version_no_positive"
   end
diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index 5899acb..deea984 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -49,14 +49,24 @@ RSpec.describe Tag, type: :model do
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, 60_000]])
     end
 
-    it 'parses fully open section literals as zero to end-of-video' do
+    it 'treats fully open section literals as plain tags' do
       result = described_class.normalise_tags!(
         ['伊地知ニジカ[-]'],
         with_sections: true
       )
 
       tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
-      expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, nil]])
+      expect(result.fetch(:sections)[tag.id]).to be_nil
+    end
+
+    it 'treats [0:00-] as a plain tag' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[0:00-]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections)[tag.id]).to be_nil
     end
 
     it 'expands zero-width sections to one millisecond' do
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 7381615..d7f3473 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -36,6 +36,7 @@ RSpec.describe 'Posts API', type: :request do
             title: post.title,
             url: post.url,
             thumbnail_base: post.thumbnail_base,
+            video_ms: post.video_ms,
             tags: post.snapshot_tag_names.join(' '),
             parent_post_ids: post.snapshot_parent_post_ids.join(' '),
             original_created_from: post.original_created_from,
@@ -803,13 +804,62 @@ RSpec.describe 'Posts API', type: :request do
       )
     end
 
+    it 'creates a video post with duration' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'video post',
+        url: 'https://example.com/video-post',
+        tags: '動画 spec_tag',
+        duration: '3:00.500',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+      expect(Post.find(json.fetch('id')).video_ms).to eq(180_500)
+      expect(json.fetch('video_ms')).to eq(180_500)
+    end
+
+    it 'clears video_ms when the saved tags do not include 動画' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'non video post',
+        url: 'https://example.com/non-video-post',
+        tags: 'spec_tag',
+        duration: '3:00',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+      expect(Post.find(json.fetch('id')).video_ms).to be_nil
+    end
+
+    it 'returns validation error when a bounded section exceeds duration' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'too long section',
+        url: 'https://example.com/too-long-section',
+        tags: '動画 伊地知ニジカ[2:50-3:10]',
+        duration: '3:00',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'video_ms' => ['タグ区間の終端が動画時間を超えてゐます．']
+      )
+    end
+
     it 'saves open-ended sections with end_ms NULL' do
       sign_in_as(member)
 
       post '/posts', params: post_write_params(
         title: 'open ended section literal',
         url: 'https://example.com/open-ended-section-literal',
-        tags: '伊地知ニジカ[1:00-]',
+        tags: '動画 伊地知ニジカ[1:00-]',
+        duration: '3:00',
         thumbnail: dummy_upload
       )
 
@@ -823,7 +873,7 @@ RSpec.describe 'Posts API', type: :request do
       expect(section.end_ms).to be_nil
     end
 
-    it 'treats [-] as [0:00-] and saves end_ms NULL' do
+    it 'does not save sections for [-]' do
       sign_in_as(member)
 
       post '/posts', params: post_write_params(
@@ -837,10 +887,24 @@ RSpec.describe 'Posts API', type: :request do
 
       created_post = Post.find(json.fetch('id'))
       tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
-      section = PostTagSection.find_by!(post: created_post, tag:)
+      expect(PostTagSection.find_by(post: created_post, tag:)).to be_nil
+    end
 
-      expect(section.begin_ms).to eq(0)
-      expect(section.end_ms).to be_nil
+    it 'does not save sections for [0:00-]' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'zero open ended section literal',
+        url: 'https://example.com/zero-open-ended-section-literal',
+        tags: '伊地知ニジカ[0:00-]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+
+      created_post = Post.find(json.fetch('id'))
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      expect(PostTagSection.find_by(post: created_post, tag:)).to be_nil
     end
 
     it 'returns end_ms null for open-ended sections in show response' do
@@ -849,7 +913,8 @@ RSpec.describe 'Posts API', type: :request do
       post '/posts', params: post_write_params(
         title: 'show open ended section literal',
         url: 'https://example.com/show-open-ended-section-literal',
-        tags: '伊地知ニジカ[1:00-]',
+        tags: '動画 伊地知ニジカ[1:00-]',
+        duration: '3:00',
         thumbnail: dummy_upload
       )
 
@@ -864,6 +929,37 @@ RSpec.describe 'Posts API', type: :request do
       ])
     end
 
+    it 'allows open-ended sections when begin is within duration' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'valid open ended section literal',
+        url: 'https://example.com/valid-open-ended-section-literal',
+        tags: '動画 伊地知ニジカ[1:00-]',
+        duration: '3:00',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+    end
+
+    it 'rejects open-ended sections when begin equals duration' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'invalid open ended section literal',
+        url: 'https://example.com/invalid-open-ended-section-literal',
+        tags: '動画 伊地知ニジカ[3:00-]',
+        duration: '3:00',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'video_ms' => ['タグ区間の開始が動画時間以上です．']
+      )
+    end
+
     context "when nico tag already exists in tags" do
       before do
         Tag.find_undiscard_or_create_by!(
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 1ed75bd..c1fdd72 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react'
+import { useEffect, useMemo, useState } from 'react'
 
 import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
@@ -17,7 +17,10 @@ import type { FC, FormEvent } from 'react'
 import type { Post, TagWithSections } from '@/types'
 
 type PostFormField =
-    'parentPostIds' | 'tags' | 'originalCreatedAt'
+    'parentPostIds' | 'tags' | 'videoMs' | 'originalCreatedAt'
+
+const videoMsToDurationValue = (videoMs: number | null): string =>
+    videoMs == null ? '' : String (videoMs / 1_000)
 
 
 const tagsToStr = (tags: TagWithSections[]): string => {
@@ -44,6 +47,7 @@ type Props = { post:    Post
 
 const PostEditForm: FC<Props> = ({ post, onSave }) => {
   const [disabled, setDisabled] = useState (false)
+  const [duration, setDuration] = useState<string> (videoMsToDurationValue (post.videoMs))
   const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
       useValidationErrors<PostFormField> ()
   const [originalCreatedBefore, setOriginalCreatedBefore] =
@@ -55,6 +59,10 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
   const [tags, setTags] = useState<string> ('')
   const [title, setTitle] = useState (post.title)
 
+  const videoFlg =
+      useMemo (() => tags.split (/\s+/).some (tag => tag.replace (/\[.*\]$/, '') === '動画'),
+	       [tags])
+
   const dialogue = useDialogue ()
 
   const update = async (...args: Parameters<typeof updatePost>) => {
@@ -66,6 +74,7 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
       onSave ({ ...post,
 		versionNo:              data.versionNo,
 		title:                  data.title,
+		videoMs:                data.videoMs,
 		tags:                   data.tags,
 		parentPosts:            data.parentPosts,
 		childPosts:             data.childPosts,
@@ -105,6 +114,7 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 	{
 	  // TODO: 差分 UI
 	  await update ({ id: post.id, title, tags, parentPostIds,
+			  duration: videoFlg ? duration : null,
 			  originalCreatedFrom, originalCreatedBefore },
 			{ baseVersionNo: post.versionNo, merge: true })
 	  return
@@ -113,6 +123,7 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
       if (action === 'overwrite')
 	{
 	  await update ({ id: post.id, title, tags, parentPostIds,
+			  duration: videoFlg ? duration : null,
 			  originalCreatedFrom, originalCreatedBefore },
 			{ baseVersionNo: post.versionNo, force: true })
 	  return
@@ -127,6 +138,7 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
     try
     {
       await update ({ id: post.id, title, tags, parentPostIds,
+		      duration: videoFlg ? duration : null,
 		      originalCreatedFrom, originalCreatedBefore },
 		    { baseVersionNo: post.versionNo })
     }
@@ -138,8 +150,14 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 
   useEffect (() => {
     setTags (tagsToStr (post.tags))
+    setDuration (videoMsToDurationValue (post.videoMs))
   }, [post])
 
+  useEffect (() => {
+    if (!(videoFlg))
+      setDuration ('')
+  }, [videoFlg])
+
   return (
       <form onSubmit={handleSubmit} className="max-w-xl pt-2 space-y-4">
 	<FieldError messages={baseErrors}/>
@@ -152,7 +170,7 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 		  disabled={disabled}
 		  className={inputClass (invalid)}
 		  value={title ?? ''}
-		  onChange={ev => setTitle (ev.target.value)}/>)}
+		  onChange={e => setTitle (e.target.value)}/>)}
 	</FormField>
 
 	{/* 親投稿 */}
@@ -184,6 +202,20 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 	    setOriginalCreatedBefore={setOriginalCreatedBefore}
 	    errors={fieldErrors.originalCreatedAt}/>
 
+	{/* 動画時間 */}
+	{videoFlg && (
+	    <FormField label="動画時間" messages={fieldErrors.videoMs}>
+	      {({ invalid }) => (
+		  <input
+		      type="number"
+		      min="0.001"
+		      step="0.001"
+		      disabled={disabled}
+		      className={inputClass (invalid)}
+		      value={duration}
+		      onChange={e => setDuration (e.target.value)}/>)}
+	    </FormField>)}
+
 	{/* 送信 */}
 	<Button type="submit" disabled={disabled}>
 	  更新
@@ -191,4 +223,5 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
       </form>)
 }
 
+
 export default PostEditForm
diff --git a/frontend/src/lib/posts.ts b/frontend/src/lib/posts.ts
index a1febff..3134bb5 100644
--- a/frontend/src/lib/posts.ts
+++ b/frontend/src/lib/posts.ts
@@ -46,6 +46,7 @@ export const updatePost = async (
     post: { id:                     number
 	    title:                  string | null
 	    tags:                   string
+	    duration:               string | null
 	    parentPostIds:          string
 	    originalCreatedFrom:    string | null
 	    originalCreatedBefore:  string | null },
@@ -58,6 +59,7 @@ export const updatePost = async (
 	`/posts/${ post.id }`,
 	{ title: post.title,
 	  tags: post.tags,
+	  duration: post.duration,
 	  parent_post_ids: post.parentPostIds,
 	  original_created_from: post.originalCreatedFrom,
 	  original_created_before: post.originalCreatedBefore },
diff --git a/frontend/src/lib/utils.test.ts b/frontend/src/lib/utils.test.ts
index c85e150..3bdc74e 100644
--- a/frontend/src/lib/utils.test.ts
+++ b/frontend/src/lib/utils.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
-import { cn, originalCreatedAtString, toDate } from '@/lib/utils'
+import { cn, msToTime, originalCreatedAtString, toDate } from '@/lib/utils'
 
 describe ('utils', () => {
   it ('converts strings to dates and leaves date instances intact', () => {
@@ -26,3 +26,14 @@ describe ('utils', () => {
     ).toContain ('時刻不詳')
   })
 })
+
+describe ('msToTime', () => {
+  it ('keeps milliseconds when present', () => {
+    expect (msToTime (60_500)).toBe ('1:00.500')
+    expect (msToTime (60_001)).toBe ('1:00.001')
+  })
+
+  it ('omits milliseconds when they are zero', () => {
+    expect (msToTime (60_000)).toBe ('1:00')
+  })
+})
diff --git a/frontend/src/lib/utils.ts b/frontend/src/lib/utils.ts
index 5e31026..c8d30d9 100644
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@@ -78,10 +78,14 @@ export const msToTime = (ms: number): string => {
   const s = String (totalS % 60)
   const min = String (Math.trunc (totalS / 60) % 60)
   const h = Math.trunc (totalS / 3_600)
+  const remainderMs = ms % 1_000
 
-  return (h > 0
-	  ? `${ h }:${ min.padStart (2, '0') }:${ s.padStart (2, '0') }`
-	  : `${ min }:${ s.padStart (2, '0') }`)
+  const base =
+      (h > 0
+       ? `${ h }:${ min.padStart (2, '0') }:${ s.padStart (2, '0') }`
+       : `${ min }:${ s.padStart (2, '0') }`)
+
+  return remainderMs > 0 ? `${ base }.${ remainderMs.toString ().padStart (3, '0') }` : base
 }
 
 
diff --git a/frontend/src/pages/posts/PostHistoryPage.tsx b/frontend/src/pages/posts/PostHistoryPage.tsx
index 5dd3d4f..c583d78 100644
--- a/frontend/src/pages/posts/PostHistoryPage.tsx
+++ b/frontend/src/pages/posts/PostHistoryPage.tsx
@@ -15,7 +15,7 @@ import { SITE_TITLE } from '@/config'
 import { fetchPostChanges, updatePost } from '@/lib/posts'
 import { postsKeys, tagsKeys } from '@/lib/queryKeys'
 import { fetchTag } from '@/lib/tags'
-import { cn, dateString, originalCreatedAtString } from '@/lib/utils'
+import { cn, dateString, msToTime, originalCreatedAtString } from '@/lib/utils'
 
 import type { FC, MouseEvent } from 'react'
 
@@ -91,9 +91,13 @@ const PostHistoryPage: FC = () => {
 	  .filter (p => p.type !== 'removed')
 	  .map (p => p.id)
 	  .join (' ')
+      const duration =
+	  change.videoMs.current == null
+	  ? null
+	  : msToTime (change.videoMs.current)
       const originalCreatedFrom = change.originalCreatedFrom.current
       const originalCreatedBefore = change.originalCreatedBefore.current
-      await updatePost ({ id, title, tags, parentPostIds,
+      await updatePost ({ id, title, tags, duration, parentPostIds,
 			  originalCreatedFrom, originalCreatedBefore },
 		        { force: true })
 
diff --git a/frontend/src/pages/posts/PostNewPage.tsx b/frontend/src/pages/posts/PostNewPage.tsx
index f5915db..03a433c 100644
--- a/frontend/src/pages/posts/PostNewPage.tsx
+++ b/frontend/src/pages/posts/PostNewPage.tsx
@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useState, useRef } from 'react'
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useNavigate } from 'react-router-dom'
 
@@ -25,7 +25,7 @@ import type { User } from '@/types'
 type Props = { user: User | null }
 
 type PostFormField =
-    'url' | 'title' | 'tags' | 'parentPostIds' | 'originalCreatedAt' | 'thumbnail'
+    'url' | 'title' | 'tags' | 'parentPostIds' | 'videoMs' | 'originalCreatedAt' | 'thumbnail'
 
 
 const PostNewPage: FC<Props> = ({ user }) => {
@@ -40,6 +40,7 @@ const PostNewPage: FC<Props> = ({ user }) => {
   const [originalCreatedFrom, setOriginalCreatedFrom] = useState<string | null> (null)
   const [parentPostIds, setParentPostIds] = useState ('')
   const [tags, setTags] = useState ('')
+  const [duration, setDuration] = useState ('')
   const [thumbnailAutoFlg, setThumbnailAutoFlg] = useState (true)
   const [thumbnailFile, setThumbnailFile] = useState<File | null> (null)
   const [thumbnailLoading, setThumbnailLoading] = useState (false)
@@ -51,6 +52,9 @@ const PostNewPage: FC<Props> = ({ user }) => {
 
   const previousURLRef = useRef ('')
   const thumbnailPreviewRef = useRef ('')
+  const videoFlg =
+      useMemo (() => tags.split (/\s+/).some (tag => tag.replace (/\[.*\]$/, '') === '動画'),
+               [tags])
 
   const handleSubmit = async () => {
     clearValidationErrors ()
@@ -60,6 +64,8 @@ const PostNewPage: FC<Props> = ({ user }) => {
     formData.append ('url', url)
     formData.append ('tags', tags)
     formData.append ('parent_post_ids', parentPostIds)
+    if (videoFlg && duration !== '')
+      formData.append ('duration', duration)
     if (thumbnailFile)
       formData.append ('thumbnail', thumbnailFile)
     if (originalCreatedFrom)
@@ -129,6 +135,11 @@ const PostNewPage: FC<Props> = ({ user }) => {
       fetchThumbnail ()
   }, [fetchThumbnail, thumbnailAutoFlg, url])
 
+  useEffect (() => {
+    if (!(videoFlg))
+      setDuration ('')
+  }, [videoFlg])
+
   if (!(editable))
     return <Forbidden/>
 
@@ -233,6 +244,20 @@ const PostNewPage: FC<Props> = ({ user }) => {
 	      setOriginalCreatedBefore={setOriginalCreatedBefore}
 	      errors={fieldErrors.originalCreatedAt}/>
 
+	  {/* 動画時間 */}
+	  {(videoFlg &&
+	      <FormField label="動画時間" messages={fieldErrors.videoMs}>
+		{({ invalid }) => (
+		    <input
+			type="number"
+			min="0.001"
+			step="0.001"
+			value={duration}
+			onChange={e => setDuration (e.target.value)}
+			aria-invalid={invalid}
+			className={inputClass (invalid)}/>)}
+	      </FormField>)}
+
 	  {/* 送信 */}
 	  <Button onClick={handleSubmit}
 		  className="px-4 py-2 bg-blue-600 text-white rounded disabled:bg-gray-400"
diff --git a/frontend/src/test/factories.ts b/frontend/src/test/factories.ts
index 0222e48..59a068d 100644
--- a/frontend/src/test/factories.ts
+++ b/frontend/src/test/factories.ts
@@ -35,6 +35,7 @@ export const buildPost = (overrides: Partial<Post> = {}): Post => ({
   title:                 'テスト投稿',
   thumbnail:             'https://example.com/thumb.jpg',
   thumbnailBase:         null,
+  videoMs:               null,
   tags:                  [buildTag ()],
   parentPosts:           [],
   childPosts:            [],
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index 6b37dc0..1b8423b 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -140,6 +140,7 @@ export type Post = {
     title:                  string | null
     thumbnail:              string | null
     thumbnailBase:          string | null
+    videoMs:                number | null
     postSimilarityEdges?:   {
 			      targetPostId: number
 			      cos:          number
@@ -172,6 +173,7 @@ export type PostVersion = {
     url:                    { current: string; prev: string | null }
     thumbnail:              { current: string | null; prev: string | null }
     thumbnailBase:          { current: string | null; prev: string | null }
+    videoMs:                { current: number | null; prev: number | null }
     tags:                   { name: string
 			      type: 'context' | 'added' | 'removed' }[]
     parentPosts:            { id: number
-- 
2.34.1


From 881e940e24f813724808abef550fc43aa093315f Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Fri, 3 Jul 2026 02:58:10 +0900
Subject: [PATCH 6/7] #351

---
 backend/spec/requests/posts_spec.rb              | 16 ++++++++++++++++
 frontend/src/lib/posts.test.ts                   |  2 ++
 .../pages/theatres/TheatreDetailPage.test.tsx    | 12 ++++++++----
 frontend/src/types.ts                            |  7 ++++---
 4 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 8f51753..752ac6a 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -898,6 +898,22 @@ RSpec.describe 'Posts API', type: :request do
       expect(json.fetch('video_ms')).to eq(180_500)
     end
 
+    it 'creates a video post with number input duration seconds' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'video post seconds',
+        url: 'https://example.com/video-post-seconds',
+        tags: '動画 spec_tag',
+        duration: '180.5',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+      expect(Post.find(json.fetch('id')).video_ms).to eq(180_500)
+      expect(json.fetch('video_ms')).to eq(180_500)
+    end
+
     it 'clears video_ms when the saved tags do not include 動画' do
       sign_in_as(member)
 
diff --git a/frontend/src/lib/posts.test.ts b/frontend/src/lib/posts.test.ts
index 724afe4..600df31 100644
--- a/frontend/src/lib/posts.test.ts
+++ b/frontend/src/lib/posts.test.ts
@@ -70,6 +70,7 @@ describe ('posts API functions', () => {
           id:                    5,
           title:                 'new title',
           tags:                  'tag',
+          duration:              null,
           parentPostIds:         '1 2',
           originalCreatedFrom:   null,
           originalCreatedBefore: '2026-01-02T00:00:00Z',
@@ -82,6 +83,7 @@ describe ('posts API functions', () => {
         {
           title:                   'new title',
           tags:                    'tag',
+          duration:                null,
           parent_post_ids:         '1 2',
           original_created_from:   null,
           original_created_before: '2026-01-02T00:00:00Z',
diff --git a/frontend/src/pages/theatres/TheatreDetailPage.test.tsx b/frontend/src/pages/theatres/TheatreDetailPage.test.tsx
index ccb5407..2c87aba 100644
--- a/frontend/src/pages/theatres/TheatreDetailPage.test.tsx
+++ b/frontend/src/pages/theatres/TheatreDetailPage.test.tsx
@@ -88,6 +88,10 @@ const weights = buildTheatrePostSelectionWeights ({
     tags:    [],
   }],
 })
+const watchingUsers = [
+  { id: 1, name: 'tester' },
+  { id: 2, name: 'another' },
+]
 
 const renderPage = (user = buildUser ({ id: 1, role: 'member' })) =>
   renderWithProviders (
@@ -136,11 +140,11 @@ const mockDefaultApi = () => {
         postId:        currentPost.id,
         postStartedAt: '2026-01-02T03:04:05.000Z',
         postElapsedMs: 1_000,
-        watchingUsers: [{ id: 1, name: 'tester' }],
+        watchingUsers,
         skipVote:      {
           votesCount:         0,
           requiredCount:      2,
-          watchingUsersCount: 1,
+          watchingUsersCount: watchingUsers.length,
           voted:              false,
         },
       }))
@@ -150,11 +154,11 @@ const mockDefaultApi = () => {
         postId:        currentPost.id,
         postStartedAt: '2026-01-02T03:04:05.000Z',
         postElapsedMs: 2_000,
-        watchingUsers: [{ id: 1, name: 'tester' }],
+        watchingUsers,
         skipVote:      {
           votesCount:         1,
           requiredCount:      2,
-          watchingUsersCount: 1,
+          watchingUsersCount: watchingUsers.length,
           voted:              true,
         },
       }))
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index 434a579..2b9b718 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -356,6 +356,7 @@ export type Tag = {
     hasWiki:        boolean
     materialId:     number | null
     hasDeerjikists: boolean
+    children?:      Tag[]
     matchedAlias?:  string | null }
 
 export type TagVersion = {
@@ -370,9 +371,9 @@ export type TagVersion = {
     createdAt:              string
     createdByUser:          { id: number; name: string | null } | null }
 
-export type TagWithSections = Tag & { sections: { beginMs:  number
-						  endMs:    number | null }[]
-			              children: TagWithSections[] }
+export type TagWithSections = Omit<Tag, 'children'> & { sections: { beginMs:  number
+								    endMs:    number | null }[]
+					              children: TagWithSections[] }
 
 export type Theatre = {
     id:             number
-- 
2.34.1


From c7e60c9e43f117bc1f6b5eb5d64182b16d0d5328 Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Fri, 3 Jul 2026 03:20:48 +0900
Subject: [PATCH 7/7] #351

---
 frontend/src/components/PostEditForm.test.tsx | 23 +++++++++++++++++++
 frontend/src/components/PostEditForm.tsx      |  5 ----
 frontend/src/pages/posts/PostNewPage.test.tsx | 18 +++++++++++++++
 frontend/src/pages/posts/PostNewPage.tsx      |  5 ----
 4 files changed, 41 insertions(+), 10 deletions(-)

diff --git a/frontend/src/components/PostEditForm.test.tsx b/frontend/src/components/PostEditForm.test.tsx
index 1fc58a9..2ff28b1 100644
--- a/frontend/src/components/PostEditForm.test.tsx
+++ b/frontend/src/components/PostEditForm.test.tsx
@@ -66,4 +66,27 @@ describe ('PostEditForm', () => {
     expect (onSave).toHaveBeenCalledWith (expect.objectContaining ({ versionNo: 5 }))
     expect (toastApi.toast).toHaveBeenCalledWith ({ description: '更新しました．' })
   })
+
+  it ('preserves duration while the video tag is temporarily removed', () => {
+    const post = buildPost ({
+      videoMs: 180_500,
+      tags:    [
+        buildTag ({ id: 1, name: '動画', category: 'general' }),
+        buildTag ({ id: 2, name: 'general-tag', category: 'general' }),
+      ],
+    })
+
+    render (<PostEditForm post={post} onSave={vi.fn ()}/>)
+
+    expect (screen.getByRole ('spinbutton')).toHaveValue (180.5)
+
+    const tags = screen.getAllByRole ('textbox')[2]
+    fireEvent.change (tags, { target: { value: 'general-tag' } })
+    expect (screen.queryByRole ('spinbutton')).not.toBeInTheDocument ()
+
+    fireEvent.change (tags, {
+      target: { value: '動画 general-tag' },
+    })
+    expect (screen.getByRole ('spinbutton')).toHaveValue (180.5)
+  })
 })
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index c1fdd72..744c132 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -153,11 +153,6 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
     setDuration (videoMsToDurationValue (post.videoMs))
   }, [post])
 
-  useEffect (() => {
-    if (!(videoFlg))
-      setDuration ('')
-  }, [videoFlg])
-
   return (
       <form onSubmit={handleSubmit} className="max-w-xl pt-2 space-y-4">
 	<FieldError messages={baseErrors}/>
diff --git a/frontend/src/pages/posts/PostNewPage.test.tsx b/frontend/src/pages/posts/PostNewPage.test.tsx
index b8c909e..1402ed0 100644
--- a/frontend/src/pages/posts/PostNewPage.test.tsx
+++ b/frontend/src/pages/posts/PostNewPage.test.tsx
@@ -62,6 +62,24 @@ describe ('PostNewPage', () => {
     expect (toastApi.toast).toHaveBeenCalledWith ({ title: '投稿成功!' })
   })
 
+  it ('preserves duration while the video tag is temporarily removed', () => {
+    api.apiGet.mockResolvedValue ([])
+
+    renderWithProviders (<PostNewPage user={buildUser ({ role: 'member' })}/>)
+
+    const tags = screen.getAllByRole ('textbox')[3]
+    fireEvent.change (tags, { target: { value: '動画' } })
+    fireEvent.change (screen.getByRole ('spinbutton'), { target: { value: '180.5' } })
+
+    fireEvent.change (tags, { target: { value: 'general-tag' } })
+    expect (screen.queryByRole ('spinbutton')).not.toBeInTheDocument ()
+
+    fireEvent.change (tags, {
+      target: { value: '動画 general-tag' },
+    })
+    expect (screen.getByRole ('spinbutton')).toHaveValue (180.5)
+  })
+
   it ('shows 422 validation errors for post fields', async () => {
     api.apiGet.mockResolvedValue ([])
     api.isApiError.mockReturnValue (true)
diff --git a/frontend/src/pages/posts/PostNewPage.tsx b/frontend/src/pages/posts/PostNewPage.tsx
index 03a433c..0a99dc5 100644
--- a/frontend/src/pages/posts/PostNewPage.tsx
+++ b/frontend/src/pages/posts/PostNewPage.tsx
@@ -135,11 +135,6 @@ const PostNewPage: FC<Props> = ({ user }) => {
       fetchThumbnail ()
   }, [fetchThumbnail, thumbnailAutoFlg, url])
 
-  useEffect (() => {
-    if (!(videoFlg))
-      setDuration ('')
-  }, [videoFlg])
-
   if (!(editable))
     return <Forbidden/>
 
-- 
2.34.1