src/controller/subtitle-stream-controller.js

/*
 * Subtitle Stream Controller
*/

import Event from '../events';
import { logger } from '../utils/logger';
import Decrypter from '../crypt/decrypter';
import TaskLoop from '../task-loop';

const State = {
  STOPPED: 'STOPPED',
  IDLE: 'IDLE',
  KEY_LOADING: 'KEY_LOADING',
  FRAG_LOADING: 'FRAG_LOADING'
};

class SubtitleStreamController extends TaskLoop {
  constructor (hls) {
    super(hls,
      Event.MEDIA_ATTACHED,
      Event.ERROR,
      Event.KEY_LOADED,
      Event.FRAG_LOADED,
      Event.SUBTITLE_TRACKS_UPDATED,
      Event.SUBTITLE_TRACK_SWITCH,
      Event.SUBTITLE_TRACK_LOADED,
      Event.SUBTITLE_FRAG_PROCESSED);

    this.config = hls.config;
    this.vttFragSNsProcessed = {};
    this.vttFragQueues = undefined;
    this.currentlyProcessing = null;
    this.state = State.STOPPED;
    this.currentTrackId = -1;
    this.decrypter = new Decrypter(hls.observer, hls.config);
  }

  onHandlerDestroyed () {
    this.state = State.STOPPED;
  }

  // Remove all queued items and create a new, empty queue for each track.
  clearVttFragQueues () {
    this.vttFragQueues = {};
    this.tracks.forEach(track => {
      this.vttFragQueues[track.id] = [];
    });
  }

  // If no frag is being processed and queue isn't empty, initiate processing of next frag in line.
  nextFrag () {
    if (this.currentlyProcessing === null && this.currentTrackId > -1 && this.vttFragQueues[this.currentTrackId].length) {
      let frag = this.currentlyProcessing = this.vttFragQueues[this.currentTrackId].shift();
      this.fragCurrent = frag;
      this.hls.trigger(Event.FRAG_LOADING, { frag: frag });
      this.state = State.FRAG_LOADING;
    }
  }

  // When fragment has finished processing, add sn to list of completed if successful.
  onSubtitleFragProcessed (data) {
    if (data.success)
      this.vttFragSNsProcessed[data.frag.trackId].push(data.frag.sn);

    this.currentlyProcessing = null;
    this.state = State.IDLE;
    this.nextFrag();
  }

  onMediaAttached () {
    this.state = State.IDLE;
  }

  // If something goes wrong, procede to next frag, if we were processing one.
  onError (data) {
    let frag = data.frag;
    // don't handle frag error not related to subtitle fragment
    if (frag && frag.type !== 'subtitle')
      return;

    if (this.currentlyProcessing) {
      this.currentlyProcessing = null;
      this.nextFrag();
    }
  }

  doTick () {
    switch (this.state) {
    case State.IDLE:
      const tracks = this.tracks;
      let trackId = this.currentTrackId;

      const processedFragSNs = this.vttFragSNsProcessed[trackId],
        fragQueue = this.vttFragQueues[trackId],
        currentFragSN = this.currentlyProcessing ? this.currentlyProcessing.sn : -1;

      const alreadyProcessed = function (frag) {
        return processedFragSNs.indexOf(frag.sn) > -1;
      };

      const alreadyInQueue = function (frag) {
        return fragQueue.some(fragInQueue => { return fragInQueue.sn === frag.sn; });
      };

        // exit if tracks don't exist
      if (!tracks)
        break;

      var trackDetails;

      if (trackId < tracks.length)
        trackDetails = tracks[trackId].details;

      if (typeof trackDetails === 'undefined')
        break;

      // Add all fragments that haven't been, aren't currently being and aren't waiting to be processed, to queue.
      trackDetails.fragments.forEach(frag => {
        if (!(alreadyProcessed(frag) || frag.sn === currentFragSN || alreadyInQueue(frag))) {
          // Load key if subtitles are encrypted
          if ((frag.decryptdata && frag.decryptdata.uri != null) && (frag.decryptdata.key == null)) {
            logger.log(`Loading key for ${frag.sn}`);
            this.state = State.KEY_LOADING;
            this.hls.trigger(Event.KEY_LOADING, { frag: frag });
          } else {
            // Frags don't know their subtitle track ID, so let's just add that...
            frag.trackId = trackId;
            fragQueue.push(frag);
            this.nextFrag();
          }
        }
      });
    }
  }

  // Got all new subtitle tracks.
  onSubtitleTracksUpdated (data) {
    logger.log('subtitle tracks updated');
    this.tracks = data.subtitleTracks;
    this.clearVttFragQueues();
    this.vttFragSNsProcessed = {};
    this.tracks.forEach(track => {
      this.vttFragSNsProcessed[track.id] = [];
    });
  }

  onSubtitleTrackSwitch (data) {
    this.currentTrackId = data.id;
    if (this.currentTrackId === -1)
      return;

    // Check if track was already loaded and if so make sure we finish
    // downloading its frags, if not all have been downloaded yet
    const currentTrack = this.tracks[this.currentTrackId];
    let details = currentTrack.details;
    if (details !== undefined)
      this.tick();
  }

  // Got a new set of subtitle fragments.
  onSubtitleTrackLoaded () {
    this.tick();
  }

  onKeyLoaded () {
    if (this.state === State.KEY_LOADING) {
      this.state = State.IDLE;
      this.tick();
    }
  }

  onFragLoaded (data) {
    let fragCurrent = this.fragCurrent,
      decryptData = data.frag.decryptdata;
    let fragLoaded = data.frag,
      hls = this.hls;
    if (this.state === State.FRAG_LOADING &&
        fragCurrent &&
        data.frag.type === 'subtitle' &&
        fragCurrent.sn === data.frag.sn) {
      // check to see if the payload needs to be decrypted
      if ((data.payload.byteLength > 0) && (decryptData != null) && (decryptData.key != null) && (decryptData.method === 'AES-128')) {
        let startTime;
        try {
          startTime = performance.now();
        } catch (error) {
          startTime = Date.now();
        }
        // decrypt the subtitles
        this.decrypter.decrypt(data.payload, decryptData.key.buffer, decryptData.iv.buffer, function (decryptedData) {
          let endTime;
          try {
            endTime = performance.now();
          } catch (error) {
            endTime = Date.now();
          }
          hls.trigger(Event.FRAG_DECRYPTED, { frag: fragLoaded, payload: decryptedData, stats: { tstart: startTime, tdecrypt: endTime } });
        });
      }
    }
  }
}
export default SubtitleStreamController;