Merge branch 'main' into feature/386

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
@@ -45,7 +49,9 @@ 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 +103,9 @@ 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 +118,9 @@ 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
@@ -125,7 +135,7 @@ class PostsController < ApplicationController
                                  child_posts:,
                                  sibling_posts:,
                                  related:)
-                         .merge(tags: build_tag_tree_for(post.tags))
+                         .merge(tags: build_tag_tree_for(post))
   end
 
   def create
@@ -149,11 +159,15 @@ class PostsController < ApplicationController
     ApplicationRecord.transaction do
       post.save!
 
-      tags = Tag.normalise_tags!(tag_names, deny_deprecated: true)
+      Tag.normalise_tags!(tag_names, deny_deprecated: true, with_sections: true) =>
+          { tags:, sections: }
       TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
 
       tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
-      sync_post_tags!(post, tags)
+      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)
 
@@ -166,6 +180,10 @@ 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 VideoMsParseError
+    render_validation_error fields: { video_ms: ['動画時間の記法が不正です．'] }
   rescue MiniMagick::Error
     render_validation_error fields: { thumbnail: ['サムネイル画像の変換に失敗しました．'] }
   rescue ArgumentError => e
@@ -224,6 +242,8 @@ 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 =
@@ -254,12 +274,16 @@ 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
     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 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
@@ -358,7 +382,7 @@ 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
@@ -377,13 +401,21 @@ 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
+  def build_tag_tree_for post
-    tags = 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)
@@ -398,6 +430,9 @@ class PostsController < ApplicationController
     root_ids = tag_ids - child_ids
 
     tags_by_id = tags.index_by(&: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 = { }
 
@@ -405,8 +440,10 @@ class PostsController < ApplicationController
       tag = tags_by_id[tag_id]
       return nil unless tag
 
+      sections = sections_by_tag_id.fetch(tag_id, [])
+
       if path.include?(tag_id)
-        return TagRepr.inline(tag).merge(children: [])
+        return TagRepr.inline(tag).merge(children: [], sections:)
       end
 
       if memo.key?(tag_id)
@@ -418,7 +455,7 @@ class PostsController < ApplicationController
 
       children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
 
-      memo[tag_id] = TagRepr.inline(tag).merge(children:)
+      memo[tag_id] = TagRepr.inline(tag).merge(children:, sections:)
     end
 
     root_ids.filter_map { |id| build_node.call(id, []) }
@@ -487,6 +524,7 @@ 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),
@@ -499,6 +537,7 @@ 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),
@@ -506,16 +545,41 @@ class PostsController < ApplicationController
   end
 
   def editable_tag_names_from_post post
-    post.tags.not_nico.where(deprecated_at: nil)
+    post
-        .joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+        .post_tags
+        .kept
+        .joins(tag: :tag_name)
+        .merge(Tag.not_nico)
+        .merge(Tag.where(deprecated_at: nil))
+        .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:,
-                             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
 
@@ -538,11 +602,8 @@ class PostsController < ApplicationController
     value.to_s
   end
 
-  def incoming_tag_names_for_snapshot raw_tag_names
+  def section_literal section
-    tags = Tag.normalise_tags!(raw_tag_names, with_tagme: false,
+    "[#{ Post.ms_to_time(section[0]) }-#{ section[1] ? Post.ms_to_time(section[1]) : '' }]"
-                                              deny_deprecated: true)
-
-    Tag.expand_parent_tags(tags).reject(&:deprecated?).map(&:name).uniq.sort
   end
 
   def post_conflict_json post:, base_version_no:, base_snapshot:,
@@ -563,6 +624,8 @@ 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）',
@@ -626,11 +689,14 @@ 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])
 
-    editable_tags = Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false,
+    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false,
-                                                               deny_deprecated: true)
+                                               deny_deprecated: true,
+                                               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
@@ -638,14 +704,17 @@ class PostsController < ApplicationController
     tags = readonly_tags + editable_tags
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
 
-    sync_post_tags!(post, tags)
+    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])
 
     PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
   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])]
@@ -689,4 +758,44 @@ 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

@@ -60,6 +60,7 @@ 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
@@ -83,7 +84,42 @@ 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) }-#{ section.end_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
+    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_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: {

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, numericality: { only_integer: true, greater_than: :begin_ms },
+                     allow_nil: true
+end

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

@@ -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'
@@ -105,26 +115,60 @@ class Tag < ApplicationRecord
   def self.normalise_tags! tag_names, with_tagme: true,
                                       with_no_deerjikist: true,
                                       deny_nico: true,
-                                      deny_deprecated: false
+                                      deny_deprecated: false,
+                                      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|
+      raw_name = 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 (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],
+            tag_name: name)
+      end
+
+      if name.include?('[') || name.include?(']')
+        raise SectionLiteralParseError.new(raw_name, raw_name)
+      end
+
+      name = TagName.canonicalise(name).first
+
       find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         if deny_deprecated && tag.deprecated?
           raise DeprecatedTagNormalisationError, [tag.name]
         end
 
         tag.update!(category: cat) if cat && tag.category != cat
+        next if sections_by_tag.empty?
+
+        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
 
     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
@@ -150,6 +194,45 @@ 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?
@@ -246,6 +329,32 @@ class Tag < ApplicationRecord
     end
   end
 
+  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
+
+    raise SectionLiteralParseError.new(tag_name, str) unless match
+
+    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]
+
+    total_s * 1_000 + match[:ms].to_s.ljust(3, '0')[0, 3].to_i
+  end
+
   def nico_tags_cannot_be_deprecated
     if nico? && deprecated_at.present?
       errors.add :deprecated_at, 'ニコタグは廃止できません．'

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,
@@ -18,7 +19,7 @@ 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 +53,16 @@ module PostRepr
                .merge('thumbnail' => thumbnail_url(post))
   end
 
-  def tag_json tags
+  def tag_json post
-    tags.reject(&:deprecated?).map { |tag| TagRepr.inline(tag) }
+    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

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/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

backend/db/migrate/20260622010000_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: true
+      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 'end_ms IS NULL OR begin_ms < end_ms',
+                         name: 'chk_post_tag_sections_end_ms_after_begin_ms'
+    end
+  end
+end

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

@@ -298,6 +298,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) 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"
+    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 "(`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
+
   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
@@ -331,9 +344,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_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
@@ -348,8 +364,11 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) 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
 
@@ -678,6 +697,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) 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"

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

backend/spec/factories/post_tags.rb

@@ -0,0 +1,6 @@
+FactoryBot.define do
+  factory :post_tag do
+    association :post
+    association :tag
+  end
+end

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

backend/spec/models/post_tag_spec.rb

@@ -0,0 +1,41 @@
+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
+
+    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

backend/spec/models/tag_spec.rb

@@ -19,6 +19,95 @@ 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 '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)[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
+      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

backend/spec/requests/posts_spec.rb

@@ -54,6 +54,7 @@ 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,
@@ -145,6 +146,22 @@ 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" }
@@ -845,6 +862,198 @@ 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 '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 '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)
+
+      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: '動画 伊地知ニジカ[1:00-]',
+        duration: '3:00',
+        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 'does not save sections for [-]' 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' })
+      expect(PostTagSection.find_by(post: created_post, tag:)).to be_nil
+    end
+
+    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
+      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: '動画 伊地知ニジカ[1:00-]',
+        duration: '3:00',
+        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
+
+    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/App.tsx

@@ -6,6 +6,7 @@ import { BrowserRouter,
 	 Routes,
 	 useLocation } from 'react-router-dom'
 
+import DevModeWatermark from '@/components/DevModeWatermark'
 import RouteBlockerOverlay from '@/components/RouteBlockerOverlay'
 import TopNav from '@/components/TopNav'
 import DialogueProvider from '@/components/dialogues/DialogueProvider'
@@ -145,6 +146,7 @@ const App: FC = () => {
   return (
       <>
 	<RouteBlockerOverlay/>
+	{import.meta.env.DEV && <DevModeWatermark/>}
 
 	<BrowserRouter>
 	  <DialogueProvider>
@@ -152,7 +154,7 @@ const App: FC = () => {
 	      <motion.div
 		  layout="position"
 		  transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-		  className="flex flex-col h-dvh w-full overflow-y-hidden">
+		  className="relative flex flex-col h-dvh w-full overflow-y-hidden">
 		<TopNav user={user}/>
 		<RouteTransitionWrapper user={user} setUser={setUser}/>
 	      </motion.div>

frontend/src/components/DevModeWatermark.tsx

@@ -0,0 +1,46 @@
+import nikumaru from '@/assets/fonts/nikumaru.otf'
+
+import type { FC } from 'react'
+
+
+const ROW_COUNT = 8
+const COLUMN_COUNT = 12
+
+
+const DevModeWatermark: FC = () => {
+  return (
+      <div
+	  aria-hidden="true"
+	  className="pointer-events-none select-none fixed inset-0 overflow-hidden z-0">
+	<style>{`
+	  @font-face {
+	    font-family: 'Nikumaru';
+	    src: url(${nikumaru}) format('opentype');
+	  }
+	`}</style>
+	<div className="absolute -inset-32 flex flex-col justify-center gap-12 py-48">
+	  {Array.from ({ length: ROW_COUNT }, (_, rowIndex) => (
+	      <div
+		  key={rowIndex}
+		  className={
+		      'flex min-h-32 items-center gap-12 '
+		      + (rowIndex % 2 === 0 ? 'translate-x-0' : 'translate-x-32')
+		  }>
+		{Array.from ({ length: COLUMN_COUNT }, (_, columnIndex) => (
+		    <span
+			key={columnIndex}
+			className={
+			    'whitespace-nowrap text-3xl font-bold '
+			    + 'tracking-[0.3em] text-neutral-950/5 '
+			    + 'dark:text-white/10'
+			}
+			style={{ fontFamily: 'Nikumaru' }}>
+		      開発モード
+		    </span>))}
+	      </div>))}
+	</div>
+      </div>)
+}
+
+
+export default DevModeWatermark

frontend/src/components/DraggableDroppableTagRow.tsx

@@ -87,10 +87,13 @@ const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTa
 	    setDropRef (node)
 	  }}
 	  style={style}
-	  className={cn ('rounded select-none', over && 'ring-2 ring-offset-2')}
+	  className={cn (
+	      'min-w-0 max-w-full overflow-hidden rounded select-none',
+	      over && 'ring-2 ring-offset-2')}
 	  {...attributes}
 	  {...listeners}>
 	<motion.div
+	    className="flex min-w-0 max-w-full items-baseline overflow-hidden"
 	    transition={{ layout: { duration: .2, ease: 'easeOut' } }}
 	    layoutId={`tag-${ sp ? 'sp-' : '' }${ tag.id }`}>
 	  <TagLink tag={tag} nestLevel={nestLevel}/>
@@ -98,4 +101,4 @@ const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTa
       </div>)
 }
 
-export default DraggableDroppableTagRow
+export default DraggableDroppableTagRow

frontend/src/components/MaterialSidebar.tsx

@@ -318,12 +318,20 @@ const MobileMaterialTreeNode: FC<{ depth?: number
 	    <TagLink
 		tag={sidebarTagToTag (tag)}
 		title={tag.name}
+		truncateOnMobile
 		withCount={false}
 		withWiki={false}
 		to={materialPath (tag.id, materialFilter)}
 		className="block overflow-hidden text-ellipsis whitespace-nowrap
 			   [max-inline-size:var(--tag-link-inline-size)]
-			   [max-height:var(--tag-link-inline-size)]"/>
+			   [max-height:var(--tag-link-inline-size)]
+			   [&_.tag-marquee]:block
+			   [&_.tag-marquee]:h-full
+			   [&_.tag-marquee]:overflow-hidden
+			   [&_.tag-marquee__static]:h-full
+			   [&_.tag-marquee__static]:overflow-hidden
+			   [&_.tag-marquee__static]:text-ellipsis
+			   [&_.tag-marquee__static]:[text-overflow:ellipsis]"/>
 	  </div>
 	  {tag.hasChildren && (
 	      <button

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)
+  })
 })

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'
@@ -9,29 +9,35 @@ import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { isApiError } from '@/lib/api'
 import { updatePost } from '@/lib/posts'
-import { inputClass } from '@/lib/utils'
+import { inputClass, msToTime } from '@/lib/utils'
 import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { FC, FormEvent } from 'react'
 
-import type { Post, Tag } from '@/types'
+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: Tag[]): string => {
+const tagsToStr = (tags: TagWithSections[]): string => {
-  const result: Tag[] = []
+  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)))].join (' ')
+  return [...(new Set (result.map (t =>
+      `${ t.name }${ t.sections
+		     .map (s => `[${ msToTime (s.beginMs) }-${ s.endMs == null ? '' : msToTime (s.endMs) }]`)
+		     .join ('') }`)))].join (' ')
 }
 
 
@@ -41,6 +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] =
@@ -52,6 +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>) => {
@@ -63,6 +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,
@@ -102,6 +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
@@ -110,6 +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
@@ -124,6 +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 })
     }
@@ -134,7 +149,8 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
   }
 
   useEffect (() => {
-    setTags(tagsToStr (post.tags))
+    setTags (tagsToStr (post.tags))
+    setDuration (videoMsToDurationValue (post.videoMs))
   }, [post])
 
   return (
@@ -149,7 +165,7 @@ 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 */}
@@ -181,6 +197,20 @@ 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
@@ -188,4 +218,5 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
       </form>)
 }
 
+
 export default PostEditForm

frontend/src/components/ResponsiveMarqueeText.tsx

@@ -0,0 +1,250 @@
+import { cn } from '@/lib/utils'
+import { useEffect, useRef, useState } from 'react'
+
+import type { FC } from 'react'
+
+type Props = {
+    text:      string
+    className?: string
+    truncateOnMobile?: boolean
+    title?:    string }
+
+const DESKTOP_MARQUEE_MEDIA =
+    '(min-width: 768px) and (hover: hover) and (pointer: fine) and (prefers-reduced-motion: no-preference)'
+const MARQUEE_START_DELAY_MS = 1600
+const MARQUEE_END_HOLD_MS = 2400
+const MARQUEE_SCROLL_PX_PER_SECOND = 43
+const MIN_MARQUEE_OVERFLOW_PX = 1
+
+
+const ResponsiveMarqueeText: FC<Props> = (
+    { text, className, truncateOnMobile = false, title },
+) => {
+  const outerRef = useRef<HTMLSpanElement | null> (null)
+  const staticRef = useRef<HTMLSpanElement | null> (null)
+  const animatedRef = useRef<HTMLSpanElement | null> (null)
+  const animationRef = useRef<Animation | null> (null)
+  const timeoutRef = useRef<number | null> (null)
+  const rafRef = useRef<number | null> (null)
+  const [overflowPx, setOverflowPx] = useState (0)
+  const [desktopMarqueeEnabled, setDesktopMarqueeEnabled] = useState (false)
+  const [active, setActive] = useState (false)
+  const [marqueeVisible, setMarqueeVisible] = useState (false)
+
+  useEffect (() => {
+    const outer = outerRef.current
+    const inner = staticRef.current
+
+    if (!(outer) || !(inner))
+      return
+
+    const measure = () => {
+      const nextOverflow = Math.max (0, Math.ceil (inner.scrollWidth - outer.clientWidth))
+      setOverflowPx (prev => Math.abs (prev - nextOverflow) <= 1 ? prev : nextOverflow)
+    }
+
+    measure ()
+
+    const resizeObserver =
+	typeof ResizeObserver === 'undefined'
+	? null
+	: new ResizeObserver (() => {
+	    measure ()
+	  })
+
+    resizeObserver?.observe (outer)
+    resizeObserver?.observe (inner)
+    addEventListener ('resize', measure)
+
+    return () => {
+      resizeObserver?.disconnect ()
+      removeEventListener ('resize', measure)
+    }
+  }, [text])
+
+  useEffect (() => {
+    if (typeof window === 'undefined' || typeof window.matchMedia !== 'function')
+      return
+
+    const media = window.matchMedia (DESKTOP_MARQUEE_MEDIA)
+    const update = () => {
+      setDesktopMarqueeEnabled (media.matches)
+    }
+
+    update ()
+    media.addEventListener ('change', update)
+
+    return () => {
+      media.removeEventListener ('change', update)
+    }
+  }, [])
+
+  useEffect (() => {
+    const clearScheduled = () => {
+      if (timeoutRef.current != null)
+        {
+          clearTimeout (timeoutRef.current)
+          timeoutRef.current = null
+        }
+      if (rafRef.current != null)
+        {
+          cancelAnimationFrame (rafRef.current)
+          rafRef.current = null
+        }
+      animationRef.current?.cancel ()
+      animationRef.current = null
+    }
+
+    const animated = animatedRef.current
+    const canMarquee = (
+        active
+        && desktopMarqueeEnabled
+        && overflowPx >= MIN_MARQUEE_OVERFLOW_PX
+        && animated != null)
+
+    const resetAnimated = () => {
+      const node = animatedRef.current
+
+      animationRef.current?.cancel ()
+      animationRef.current = null
+      node?.getAnimations?.().forEach (animation => {
+        animation.cancel ()
+      })
+
+      if (!(node))
+        return
+
+      node.style.transition = 'none'
+      node.style.transform = 'translateX(0)'
+    }
+
+    if (!canMarquee)
+      {
+        clearScheduled ()
+        resetAnimated ()
+        setMarqueeVisible (false)
+        return
+      }
+
+    let cancelled = false
+
+    const sleep = (ms: number) =>
+	new Promise<void> (resolve => {
+	  timeoutRef.current = window.setTimeout (() => {
+	    timeoutRef.current = null
+	    resolve ()
+	  }, ms)
+	})
+
+    const runLoop = async () => {
+      while (!cancelled)
+        {
+          resetAnimated ()
+          setMarqueeVisible (true)
+
+          await sleep (MARQUEE_START_DELAY_MS)
+          if (cancelled || !(animatedRef.current))
+            break
+
+          const moveDurationMs =
+	      overflowPx / MARQUEE_SCROLL_PX_PER_SECOND * 1000
+          const node = animatedRef.current
+
+          if (typeof node.animate === 'function')
+            {
+              const animation = node.animate (
+		  [
+		    { transform: 'translateX(0)' },
+		    { transform: `translateX(-${ overflowPx }px)` },
+		  ],
+		  { duration: moveDurationMs, easing: 'linear', fill: 'forwards' })
+              animationRef.current = animation
+              try
+              {
+                await animation.finished
+              }
+              catch
+              {
+                break
+              }
+
+              node.style.transform = `translateX(-${ overflowPx }px)`
+              animation.cancel ()
+              if (animationRef.current === animation)
+                animationRef.current = null
+            }
+          else
+            {
+              node.style.transition = `transform ${ moveDurationMs }ms linear`
+              await new Promise<void> (resolve => {
+                rafRef.current = requestAnimationFrame (() => {
+                  rafRef.current = null
+                  node.style.transform = `translateX(-${ overflowPx }px)`
+                  resolve ()
+                })
+              })
+              await sleep (moveDurationMs)
+              node.style.transition = 'none'
+              node.style.transform = `translateX(-${ overflowPx }px)`
+            }
+
+          if (cancelled)
+            break
+
+          await sleep (MARQUEE_END_HOLD_MS)
+          if (cancelled)
+            break
+
+          resetAnimated ()
+        }
+    }
+
+    void runLoop ()
+
+    return () => {
+      cancelled = true
+      clearScheduled ()
+      resetAnimated ()
+      setMarqueeVisible (false)
+    }
+  }, [active, desktopMarqueeEnabled, overflowPx, text])
+
+  return (
+      <span
+	  ref={outerRef}
+	  title={title ?? text}
+	  onMouseEnter={() => setActive (true)}
+	  onMouseLeave={() => setActive (false)}
+	  onFocus={() => setActive (true)}
+	  onBlur={() => setActive (false)}
+	  className={cn (
+	      'tag-marquee inline-block max-w-full min-w-0 align-bottom',
+	      (truncateOnMobile
+	       ? 'overflow-hidden text-ellipsis whitespace-nowrap'
+	       : 'whitespace-normal [overflow-wrap:anywhere]'),
+	      'md:overflow-hidden md:whitespace-nowrap',
+	      className)}>
+	<span
+	    ref={staticRef}
+	    className={cn (
+		'tag-marquee__static block max-w-full',
+		(truncateOnMobile
+		 ? 'overflow-hidden text-ellipsis whitespace-nowrap'
+		 : 'whitespace-normal [overflow-wrap:anywhere]'),
+		'md:overflow-hidden md:text-ellipsis md:whitespace-nowrap',
+		marqueeVisible && 'md:opacity-0')}>
+	  {text}
+	</span>
+	{overflowPx >= MIN_MARQUEE_OVERFLOW_PX && (
+	    <span
+		ref={animatedRef}
+		aria-hidden="true"
+		className={cn (
+		    'tag-marquee__animated hidden md:block',
+		    marqueeVisible ? 'md:opacity-100' : 'md:opacity-0')}>
+	      {text}
+	    </span>)}
+      </span>)
+}
+
+export default ResponsiveMarqueeText

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>,
@@ -62,8 +62,9 @@ const renderTagTree = (
 
 
 const isDescendant = (
-    root:     Tag,
+    root:     TagWithSections,
-    targetId: number): boolean => {
+    targetId: number,
+): boolean => {
   if (!(root.children))
     return false
 
@@ -81,8 +82,9 @@ const isDescendant = (
 
 const findTag = (
     byCat:  TagByCategory,
-    id:     number): Tag | undefined => {
+    id:     number,
-  const walk = (nodes: Tag[]): Tag | undefined => {
+): TagWithSections | undefined => {
+  const walk = (nodes: TagWithSections[]): TagWithSections | undefined => {
     for (const t of nodes)
       {
 	if (t.id === id)
@@ -163,7 +165,7 @@ 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])
@@ -373,4 +375,4 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
       </SidebarComponent>)
 }
 
-export default TagDetailSidebar
+export default TagDetailSidebar

frontend/src/components/TagLink.tsx

@@ -1,4 +1,5 @@
 import PrefetchLink from '@/components/PrefetchLink'
+import ResponsiveMarqueeText from '@/components/ResponsiveMarqueeText'
 import { LIGHT_COLOUR_SHADE, DARK_COLOUR_SHADE, TAG_COLOUR } from '@/consts'
 import { cn } from '@/lib/utils'
 
@@ -9,6 +10,7 @@ import type { Tag } from '@/types'
 type CommonProps = { 
     tag:        Tag
     nestLevel?: number
+    truncateOnMobile?: boolean
     withWiki?:  boolean
     withCount?: boolean }
 
@@ -30,9 +32,11 @@ type Props =
 const TagLink: FC<Props> = ({ tag,
 			      nestLevel = 0,
 			      linkFlg   = true,
+			      truncateOnMobile = false,
 			      withWiki  = true,
 			      withCount = true,
 			      className,
+			      title,
 			      ...props }) => {
   const spanClass = cn (
       `text-${ TAG_COLOUR[tag.category] }-${ LIGHT_COLOUR_SHADE }`,
@@ -41,11 +45,18 @@ const TagLink: FC<Props> = ({ tag,
       spanClass,
       `hover:text-${ TAG_COLOUR[tag.category] }-${ LIGHT_COLOUR_SHADE - 200 }`,
       `dark:hover:text-${ TAG_COLOUR[tag.category] }-${ DARK_COLOUR_SHADE - 200 }`)
+  const textClass = 'group min-w-0 max-w-full overflow-hidden align-bottom'
+  const rootClass =
+      'inline-flex min-w-0 max-w-full flex-nowrap items-stretch align-baseline gap-x-1 md:items-baseline'
+  const markerWrapClass = 'shrink-0 self-start md:self-auto'
+  const countClass = 'shrink-0 self-end md:self-auto'
+  const textTitle = title
+      ?? (tag.matchedAlias == null ? tag.name : `${ tag.matchedAlias } → ${ tag.name }`)
 
   return (
-      <>
+      <span className={rootClass}>
 	{(linkFlg && withWiki) && (
-	    <span className="mr-1">
+	    <span className={markerWrapClass}>
 	      {(tag.materialId != null || tag.hasWiki || tag.hasDeerjikists)
 	       ? (
 		  tag.materialId == null && !(tag.hasDeerjikists)
@@ -100,33 +111,48 @@ const TagLink: FC<Props> = ({ tag,
 	    </span>)}
 	{nestLevel > 0 && (
 	    <span
-		className="ml-1 mr-1"
+		className="ml-1 mr-1 shrink-0"
 		style={{ paddingLeft: `${ (nestLevel - 1) }rem` }}>
 	      ↳
 	    </span>)}
 	{tag.matchedAlias != null && (
 	    <>
-	      <span className={cn (spanClass, className)} {...props}>
+	      <span
-		{tag.matchedAlias}
+		  title={textTitle}
+		  className={cn (spanClass, textClass, className)}
+		  {...props}>
+		<ResponsiveMarqueeText
+		    text={tag.matchedAlias}
+		    title={textTitle}
+		    truncateOnMobile={truncateOnMobile}/>
 	      </span>
-	      <> → </>
+	      <span className="shrink-0"> → </span>
 	    </>)}
 	{linkFlg
 	 ? (
 	    <PrefetchLink
 		to={`/posts?${ (new URLSearchParams ({ tags: tag.name })).toString () }`}
-		className={cn (linkClass, className)}
+		title={textTitle}
+		className={cn (linkClass, textClass, className)}
 		{...props}>
-	      {tag.name}
+	      <ResponsiveMarqueeText
+		  text={tag.name}
+		  title={textTitle}
+		  truncateOnMobile={truncateOnMobile}/>
 	    </PrefetchLink>)
 	 : (
-	    <span className={cn (spanClass, className)}
+	    <span
+		  title={textTitle}
+		  className={cn (spanClass, textClass, className)}
 		  {...props}>
-	      {tag.name}
+	      <ResponsiveMarqueeText
+		  text={tag.name}
+		  title={textTitle}
+		  truncateOnMobile={truncateOnMobile}/>
 	    </span>)}
 	{withCount && (
-	    <span className="ml-1">{tag.postCount}</span>)}
+	    <span className={countClass}>{tag.postCount}</span>)}
-      </>)
+      </span>)
 }
 
 export default TagLink

frontend/src/components/TagSearchBox.tsx

@@ -20,12 +20,14 @@ const TagSearchBox: FC<Props> = ({ suggestions, activeIndex, onSelect }) => {
 		     rounded shadow">
 	{suggestions.map ((tag, i) => (
 	    <li key={tag.id}
-		className={cn ('px-3 py-2 cursor-pointer hover:bg-gray-300 dark:hover:bg-gray-700', 
+		className={cn ('min-w-0 overflow-hidden px-3 py-2 cursor-pointer hover:bg-gray-300 dark:hover:bg-gray-700',
 			       i === activeIndex && 'bg-gray-300 dark:bg-gray-700')}
 		onMouseDown={() => onSelect (tag)}>
-	      <TagLink tag={tag} linkFlg={false} withWiki={false}/>
+	      <div className="flex min-w-0 max-w-full items-baseline overflow-hidden">
+		<TagLink tag={tag} linkFlg={false} withWiki={false}/>
+	      </div>
 	    </li>))}
       </ul>)
 }
 
-export default TagSearchBox
+export default TagSearchBox

frontend/src/components/TagSidebar.tsx

@@ -64,8 +64,9 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
 	<ul>
 	  {CATEGORIES.flatMap (cat => cat in tags ? (
 	      tags[cat].map (tag => (
-		  <li key={tag.id} className="mb-1">
+		  <li key={tag.id} className="mb-1 min-w-0 max-w-full overflow-hidden">
 		    <motion.div
+			className="flex min-w-0 max-w-full items-baseline overflow-hidden"
 			transition={{ layout: { duration: .2, ease: 'easeOut' } }}
 			layoutId={`tag-${ tag.id }`}>
 		      <TagLink tag={tag} onClick={onClick}/>
@@ -128,4 +129,4 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
       </SidebarComponent>)
 }
 
-export default TagSidebar
+export default TagSidebar

frontend/src/index.css

@@ -132,3 +132,20 @@ body
   0%, 100% { color: #f87171; }
   50% { color: #60a5fa; }
 }
+
+.tag-marquee
+{
+  position: relative;
+}
+
+.tag-marquee__animated
+{
+  position: absolute;
+  inset: 0 auto 0 0;
+  min-width: 100%;
+  width: max-content;
+  opacity: 0;
+  pointer-events: none;
+  white-space: nowrap;
+  will-change: transform;
+}

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',

frontend/src/lib/posts.ts

@@ -44,6 +44,7 @@ export const updatePost = async (
     post: { id:                     number
 	    title:                  string | null
 	    tags:                   string
+	    duration:               string | null
 	    parentPostIds:          string
 	    originalCreatedFrom:    string | null
 	    originalCreatedBefore:  string | null },
@@ -55,6 +56,7 @@ 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

@@ -71,6 +71,22 @@ export const originalCreatedAtString = (
 }
 
 
+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 = Math.trunc (totalS / 3_600)
+  const remainderMs = ms % 1_000
+
+  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
+}
+
+
 export const inputClass = (invalid?: boolean, className?: string): string =>
     cn ('w-full rounded border p-2',
 	(invalid

frontend/src/pages/posts/PostHistoryPage.tsx

@@ -91,9 +91,13 @@ const PostHistoryPage: FC = () => {
 	  .filter (p => p.type !== 'removed')
 	  .map (p => p.id)
 	  .join (' ')
+      const duration =
+	  change.videoMs.current == null
+	  ? null
+	  : String (change.videoMs.current / 1_000)
       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.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)

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)
@@ -233,6 +239,20 @@ 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/pages/theatres/TheatreDetailPage.test.tsx

@@ -1,9 +1,10 @@
-import { act, fireEvent, screen, waitFor } from '@testing-library/react'
+import { act, fireEvent, screen, waitFor, within } from '@testing-library/react'
 import { Route, Routes } from 'react-router-dom'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import TheatreDetailPage from '@/pages/theatres/TheatreDetailPage'
 import { buildPost,
+	 buildTag,
 	 buildTheatre,
 	 buildTheatreComment,
 	 buildTheatreInfo,
@@ -87,6 +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 (
@@ -96,6 +101,9 @@ const renderPage = (user = buildUser ({ id: 1, role: 'member' })) =>
       { route: '/theatres/7' },
   )
 
+const tagSection = (): HTMLElement =>
+  screen.getAllByRole ('heading', { name: 'タグ' })[0].closest ('section')!
+
 const mockDefaultApi = () => {
   api.apiGet.mockImplementation ((path: string) => {
     switch (path)
@@ -132,11 +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,
         },
       }))
@@ -146,11 +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,
         },
       }))
@@ -245,6 +253,53 @@ describe ('TheatreDetailPage', () => {
     expect (postEmbed.seek).not.toHaveBeenCalledWith (0)
   })
 
+  it ('shows child tags from the post tag tree in both vertical and horizontal layouts', async () => {
+    const childTag = buildTag ({ id: 12, name: '子タグ', category: 'general' })
+    const parentTag = buildTag ({
+      id:       11,
+      name:     '親タグ',
+      category: 'general',
+      children: [childTag],
+    })
+    const duplicateParentTag = buildTag ({
+      id:       13,
+      name:     '別親タグ',
+      category: 'general',
+      children: [childTag],
+    })
+
+    postsApi.fetchPost.mockResolvedValueOnce (buildPost ({
+      ...currentPost,
+      tags: [parentTag, duplicateParentTag],
+    }))
+
+    renderPage ()
+
+    await screen.findByText ('Embed:上映中の投稿')
+
+    expect (within (tagSection ()).getByRole ('link', { name: '親タグ' }))
+      .toBeInTheDocument ()
+    expect (within (tagSection ()).getByRole ('link', { name: '別親タグ' }))
+      .toBeInTheDocument ()
+    expect (within (tagSection ()).getAllByRole ('link', { name: '子タグ' })[0])
+      .toBeInTheDocument ()
+    expect (within (tagSection ()).getAllByText ('↳').length).toBeGreaterThan (0)
+
+    fireEvent.click (screen.getByRole ('button', { name: '2 列 A 型' }))
+    fireEvent.click (screen.getAllByRole ('button', { name: '横並び' })[0])
+
+    await waitFor (() => {
+      expect (within (tagSection ()).getByRole ('link', { name: '親タグ' }))
+	.toBeInTheDocument ()
+      expect (within (tagSection ()).getByRole ('link', { name: '別親タグ' }))
+	.toBeInTheDocument ()
+      expect (within (tagSection ()).getByRole ('link', { name: '子タグ' }))
+	.toBeInTheDocument ()
+      expect (within (tagSection ()).getAllByRole ('link', { name: '子タグ' }))
+	.toHaveLength (1)
+    })
+  })
+
   it ('does not advance host post while video length is unknown', async () => {
     api.apiPut.mockImplementation ((path: string) => {
       switch (path)

frontend/src/pages/theatres/TheatreDetailPage.tsx

@@ -102,6 +102,28 @@ const compareTagName = (a: Tag, b: Tag): number =>
     a.name === b.name ? 0 : (a.name < b.name ? -1 : 1)
 
 
+const flattenTags = (tags: Tag[]): Tag[] => {
+  const flattened: Tag[] = []
+  const seen = new Set<number> ()
+
+  const visit = (tag: Tag) => {
+    if (seen.has (tag.id))
+      return
+
+    seen.add (tag.id)
+    flattened.push (tag)
+
+    for (const child of tag.children ?? [])
+      visit (child)
+  }
+
+  for (const tag of tags)
+    visit (tag)
+
+  return flattened
+}
+
+
 const tagsByCategory = (tags: Tag[]): Partial<Record<Category, Tag[]>> => {
   const grouped: Partial<Record<Category, Tag[]>> = { }
 
@@ -118,15 +140,39 @@ const tagsByCategory = (tags: Tag[]): Partial<Record<Category, Tag[]>> => {
 }
 
 
+const renderReadonlyTagTree = (
+    tag:       Tag,
+    nestLevel: number,
+    path:      string,
+    ancestors: Set<number> = new Set<number> (),
+): ReactNode[] => {
+  const key = `${ path }-${ tag.id }`
+  const nextAncestors = new Set (ancestors)
+  nextAncestors.add (tag.id)
+
+  return [
+      (
+	  <li key={key} className="text-left leading-tight">
+	    <TagLink tag={tag} nestLevel={nestLevel} withCount={false}/>
+	  </li>),
+      ...((tag.children ?? [])
+	  .filter (child => !(nextAncestors.has (child.id)))
+	  .sort (compareTagName)
+	  .flatMap (child =>
+	      renderReadonlyTagTree (child, nestLevel + 1, key, nextAncestors)))]
+}
+
+
 const TagList: FC<{ tags: Tag[]; compact?: boolean; flow?: TagFlow }> = (
     { tags, compact, flow = 'vertical' }) => {
-  const grouped = tagsByCategory (tags)
+  const horizontalGrouped = tagsByCategory (flattenTags (tags))
+  const verticalGrouped = tagsByCategory (tags)
 
   if (flow === 'horizontal')
     {
       return (
 	  <ul className={cn ('flex flex-wrap gap-x-3 gap-y-1', compact && 'text-sm')}>
-	    {CATEGORIES.flatMap (cat => grouped[cat] ?? []).map (tag => (
+	    {CATEGORIES.flatMap (cat => horizontalGrouped[cat] ?? []).map (tag => (
 		<li key={tag.id} className="text-left leading-tight">
 		  <TagLink tag={tag} withCount={false}/>
 		</li>))}
@@ -136,7 +182,7 @@ const TagList: FC<{ tags: Tag[]; compact?: boolean; flow?: TagFlow }> = (
   return (
       <div className="space-y-3">
 	{CATEGORIES.map (cat => {
-	  const rows = grouped[cat] ?? []
+	  const rows = verticalGrouped[cat] ?? []
 	  if (rows.length === 0)
 	    return null
 
@@ -146,10 +192,8 @@ const TagList: FC<{ tags: Tag[]; compact?: boolean; flow?: TagFlow }> = (
 		  {CATEGORY_NAMES[cat]}
 		</div>
 		<ul className={cn ('space-y-1', compact && 'text-sm')}>
-		  {rows.map (tag => (
+		  {rows.flatMap (tag =>
-		      <li key={tag.id} className="text-left leading-tight">
+		      renderReadonlyTagTree (tag, 0, `cat-${ cat }`))}
-			<TagLink tag={tag} withCount={false}/>
-		      </li>))}
 		</ul>
 	      </div>)
 	})}

frontend/src/test/factories.ts

@@ -1,6 +1,6 @@
 import type { Material,
 	      Post,
-	      Tag,
+	      TagWithSections,
 	      Theatre,
 	      TheatreComment,
 	      TheatreInfo,
@@ -9,7 +9,7 @@ import type { Material,
 	      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',
@@ -23,6 +23,8 @@ export const buildTag = (overrides: Partial<Tag> = {}): Tag => ({
   materialId:     null,
   hasDeerjikists: false,
   matchedAlias:   null,
+  sections:       [],
+  children:       [],
   ...overrides,
 })
 
@@ -33,6 +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

@@ -288,11 +288,12 @@ export type Post = {
     title:                  string | null
     thumbnail:              string | null
     thumbnailBase:          string | null
+    videoMs:                number | null
     postSimilarityEdges?:   {
 			      targetPostId: number
 			      cos:          number
 			  }[]
-    tags:                   Tag[]
+    tags:                   TagWithSections[]
     parentPosts?:           Post[]
     childPosts?:            Post[]
     siblingPosts?:          Record<`${ number }`, Post[]>
@@ -320,6 +321,7 @@ 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
@@ -369,6 +371,10 @@ export type TagVersion = {
     createdAt:              string
     createdByUser:          { id: number; name: string | null } | null }
 
+export type TagWithSections = Omit<Tag, 'children'> & { sections: { beginMs:  number
+								    endMs:    number | null }[]
+					              children: TagWithSections[] }
+
 export type Theatre = {
     id:             number
     name:           string | null