#351

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,

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

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
 
+    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)

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
 

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
 

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,

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,

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

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

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

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)
+    it 'does not save sections for [0:00-]' do
-      expect(section.end_ms).to be_nil
+      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!(

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

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 },

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')
+  })
+})

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
+  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
 }
 
 

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 })
 

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"

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:            [],

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