Comments and bullet comments

Two comment systems live side by side: ordinary threaded comments, and bullet comments (danmaku), the overlay text that scrolls across the video timed to playback.

Ordinary comments

A CommentsExtractor is a ListExtractor<CommentsInfoItem>; CommentsInfo.getInfo(url) drives it like any list, with getMoreItems for pagination. It can report the whole section off via isCommentsDisabled().

A CommentsInfoItem is rich:

String getCommentText();  String getUploaderName();  String getUploaderAvatarUrl();
int getLikeCount();  String getTextualLikeCount();
boolean isPinned();  boolean isHeartedByUploader();  boolean isUploaderVerified();
int getStreamPosition();        // timestamp the comment points at, or NO_STREAM_POSITION
int getReplyCount();  Page getReplies();   // replies are their own page
Collection<Image> getPictures();

Replies are not inline: each item carries a replies Page, fetched through the same getMoreItems machinery when the user expands a thread.

Bullet comments (danmaku)

Bullet comments are a different beast, modelled for an overlay rather than a list. BulletCommentsExtractor (also a ListExtractor) adds live-aware controls:

boolean isLive();  boolean isDisabled();
List<BulletCommentsInfoItem> getLiveMessages();   // poll new ones on a live stream
void setCurrentPlayPosition(long ms);             // align the overlay to playback
void disconnect();  void reconnect();  void clearMappingState();

A BulletCommentsInfoItem describes how and when to paint one comment:

String getCommentText();
Duration getDuration();      // when in the video it appears (required)
int getArgbColor();          // ARGB32, e.g. white = 0xFFFFFFFF
Position getPosition();       // REGULAR, BOTTOM, TOP, SUPERCHAT
double getRelativeFontSize();
int getLastingTime();        // how long it stays on screen
boolean isLive();

Items are Comparable by their timestamp, so the overlay can play them back in order.

Who has them

Bullet comments are implemented by BiliBili (BilibiliBulletCommentsExtractor), NicoNico (NiconicoBulletCommentsExtractor), and YouTube live chat (YoutubeBulletCommentsExtractor). A service opts in by overriding getBulletCommentsLHFactory() / getBulletCommentsExtractor() (null by default) and declaring the BULLET_COMMENTS capability. Services without danmaku simply never expose it.