src/controller/subtitle-track-controller.js

/*
 * subtitle track controller
*/

import Event from '../events';
import EventHandler from '../event-handler';
import { logger } from '../utils/logger';

function filterSubtitleTracks (textTrackList) {
  let tracks = [];
  for (let i = 0; i < textTrackList.length; i++) {
    if (textTrackList[i].kind === 'subtitles')
      tracks.push(textTrackList[i]);
  }
  return tracks;
}

class SubtitleTrackController extends EventHandler {
  constructor (hls) {
    super(hls,
      Event.MEDIA_ATTACHED,
      Event.MEDIA_DETACHING,
      Event.MANIFEST_LOADING,
      Event.MANIFEST_LOADED,
      Event.SUBTITLE_TRACK_LOADED);
    this.tracks = [];
    this.trackId = -1;
    this.media = undefined;

    /**
     * @member {boolean} subtitleDisplay Enable/disable subtitle display rendering
     */
    this.subtitleDisplay = false;
  }

  _onTextTracksChanged () {
    // Media is undefined when switching streams via loadSource()
    if (!this.media)
      return;

    let trackId = -1;
    let tracks = filterSubtitleTracks(this.media.textTracks);
    for (let id = 0; id < tracks.length; id++) {
      if (tracks[id].mode === 'hidden') {
        // Do not break in case there is a following track with showing.
        trackId = id;
      } else if (tracks[id].mode === 'showing') {
        trackId = id;
        break;
      }
    }

    // Setting current subtitleTrack will invoke code.
    this.subtitleTrack = trackId;
  }

  destroy () {
    EventHandler.prototype.destroy.call(this);
  }

  // Listen for subtitle track change, then extract the current track ID.
  onMediaAttached (data) {
    this.media = data.media;
    if (!this.media)
      return;

    if (this.queuedDefaultTrack !== undefined) {
      this.subtitleTrack = this.queuedDefaultTrack;
      delete this.queuedDefaultTrack;
    }

    this.trackChangeListener = this._onTextTracksChanged.bind(this);

    this.useTextTrackPolling = !(this.media.textTracks && 'onchange' in this.media.textTracks);
    if (this.useTextTrackPolling) {
      this.subtitlePollingInterval = setInterval(() => {
        this.trackChangeListener();
      }, 500);
    } else {
      this.media.textTracks.addEventListener('change', this.trackChangeListener);
    }
  }

  onMediaDetaching () {
    if (!this.media)
      return;

    if (this.useTextTrackPolling)
      clearInterval(this.subtitlePollingInterval);
    else
      this.media.textTracks.removeEventListener('change', this.trackChangeListener);

    this.media = undefined;
  }

  // Reset subtitle tracks on manifest loading
  onManifestLoading () {
    this.tracks = [];
    this.trackId = -1;
  }

  // Fired whenever a new manifest is loaded.
  onManifestLoaded (data) {
    let tracks = data.subtitles || [];
    this.tracks = tracks;
    this.trackId = -1;
    this.hls.trigger(Event.SUBTITLE_TRACKS_UPDATED, { subtitleTracks: tracks });

    // loop through available subtitle tracks and autoselect default if needed
    // TODO: improve selection logic to handle forced, etc
    tracks.forEach(track => {
      if (track.default) {
        // setting this.subtitleTrack will trigger internal logic
        // if media has not been attached yet, it will fail
        // we keep a reference to the default track id
        // and we'll set subtitleTrack when onMediaAttached is triggered
        if (this.media)
          this.subtitleTrack = track.id;
        else
          this.queuedDefaultTrack = track.id;
      }
    });
  }

  // Trigger subtitle track playlist reload.
  onTick () {
    const trackId = this.trackId;
    const subtitleTrack = this.tracks[trackId];
    if (!subtitleTrack)
      return;

    const details = subtitleTrack.details;
    // check if we need to load playlist for this subtitle Track
    if (details === undefined || details.live === true) {
      // track not retrieved yet, or live playlist we need to (re)load it
      logger.log(`(re)loading playlist for subtitle track ${trackId}`);
      this.hls.trigger(Event.SUBTITLE_TRACK_LOADING, { url: subtitleTrack.url, id: trackId });
    }
  }

  onSubtitleTrackLoaded (data) {
    if (data.id < this.tracks.length) {
      logger.log(`subtitle track ${data.id} loaded`);
      this.tracks[data.id].details = data.details;
      // check if current playlist is a live playlist
      if (data.details.live && !this.timer) {
        // if live playlist we will have to reload it periodically
        // set reload period to playlist target duration
        this.timer = setInterval(() => {
          this.onTick();
        }, 1000 * data.details.targetduration, this);
      }
      if (!data.details.live && this.timer) {
        // playlist is not live and timer is armed : stopping it
        clearInterval(this.timer);
        this.timer = null;
      }
    }
  }

  /** get alternate subtitle tracks list from playlist **/
  get subtitleTracks () {
    return this.tracks;
  }

  /** get index of the selected subtitle track (index in subtitle track lists) **/
  get subtitleTrack () {
    return this.trackId;
  }

  /** select a subtitle track, based on its index in subtitle track lists**/
  set subtitleTrack (subtitleTrackId) {
    if (this.trackId !== subtitleTrackId) { // || this.tracks[subtitleTrackId].details === undefined) {
      this.setSubtitleTrackInternal(subtitleTrackId);
    }
  }

  setSubtitleTrackInternal (newId) {
    // check if level idx is valid
    if (newId < -1 || newId >= this.tracks.length)
      return;

    // stopping live reloading timer if any
    if (this.timer) {
      clearInterval(this.timer);
      this.timer = null;
    }

    let textTracks = filterSubtitleTracks(this.media.textTracks);

    // hide currently enabled subtitle track
    if (this.trackId !== -1)
      textTracks[this.trackId].mode = 'disabled';

    this.trackId = newId;
    logger.log(`switching to subtitle track ${newId}`);
    this.hls.trigger(Event.SUBTITLE_TRACK_SWITCH, { id: newId });

    if (newId === -1)
      return;

    const subtitleTrack = this.tracks[newId];
    if (newId < textTracks.length)
      textTracks[newId].mode = this.subtitleDisplay ? 'showing' : 'hidden';

    // check if we need to load playlist for this subtitle Track
    let details = subtitleTrack.details;
    if (details === undefined || details.live === true) {
      // track not retrieved yet, or live playlist we need to (re)load it
      logger.log(`(re)loading playlist for subtitle track ${newId}`);
      this.hls.trigger(Event.SUBTITLE_TRACK_LOADING, { url: subtitleTrack.url, id: newId });
    }
  }
}

export default SubtitleTrackController;