src/utils/texttrack-utils.ts

import { logger } from './logger';
 
export function sendAddTrackEvent(track: TextTrack, videoEl: HTMLMediaElement) {
  let event: Event;
  try {
    event = new Event('addtrack');
  } catch (err) {
    // for IE11
    event = document.createEvent('Event');
    event.initEvent('addtrack', false, false);
  }
  (event as any).track = track;
  videoEl.dispatchEvent(event);
}
 
export function addCueToTrack(track: TextTrack, cue: VTTCue) {
  // Sometimes there are cue overlaps on segmented vtts so the same
  // cue can appear more than once in different vtt files.
  // This avoid showing duplicated cues with same timecode and text.
  const mode = track.mode;
  if (mode === 'disabled') {
    track.mode = 'hidden';
  }
  if (track.cues && !track.cues.getCueById(cue.id)) {
    try {
      track.addCue(cue);
      if (!track.cues.getCueById(cue.id)) {
        throw new Error(`addCue is failed for: ${cue}`);
      }
    } catch (err) {
      logger.debug(`[texttrack-utils]: ${err}`);
      const textTrackCue = new (self.TextTrackCue as any)(
        cue.startTime,
        cue.endTime,
        cue.text
      );
      textTrackCue.id = cue.id;
      track.addCue(textTrackCue);
    }
  }
  if (mode === 'disabled') {
    track.mode = mode;
  }
}
 
export function clearCurrentCues(track: TextTrack) {
  // When track.mode is disabled, track.cues will be null.
  // To guarantee the removal of cues, we need to temporarily
  // change the mode to hidden
  const mode = track.mode;
  if (mode === 'disabled') {
    track.mode = 'hidden';
  }
  if (!track.cues) {
    return;
  }
  for (let i = track.cues.length; i--; ) {
    track.removeCue(track.cues[i]);
  }
  if (mode === 'disabled') {
    track.mode = mode;
  }
}
 
export function removeCuesInRange(
  track: TextTrack,
  start: number,
  end: number
) {
  const mode = track.mode;
  if (mode === 'disabled') {
    track.mode = 'hidden';
  }
  if (!track.cues || !track.cues.length) {
    return;
  }
  const cues = getCuesInRange(track.cues, start, end);
  for (let i = 0; i < cues.length; i++) {
    track.removeCue(cues[i]);
  }
  if (mode === 'disabled') {
    track.mode = mode;
  }
}
 
// Find first cue starting after given time.
// Modified version of binary search O(log(n)).
function getFirstCueIndexAfterTime(
  cues: TextTrackCueList | TextTrackCue[],
  time: number
): number {
  // If first cue starts after time, start there
  if (time < cues[0].startTime) {
    return 0;
  }
  // If the last cue ends before time there is no overlap
  const len = cues.length - 1;
  if (time > cues[len].endTime) {
    return -1;
  }
 
  let left = 0;
  let right = len;
 
  while (left <= right) {
    const mid = Math.floor((right + left) / 2);
 
    if (time < cues[mid].startTime) {
      right = mid - 1;
    } else if (time > cues[mid].startTime && left < len) {
      left = mid + 1;
    } else {
      // If it's not lower or higher, it must be equal.
      return mid;
    }
  }
  // At this point, left and right have swapped.
  // No direct match was found, left or right element must be the closest. Check which one has the smallest diff.
  return cues[left].startTime - time < time - cues[right].startTime
    ? left
    : right;
}
 
export function getCuesInRange(
  cues: TextTrackCueList | TextTrackCue[],
  start: number,
  end: number
): TextTrackCue[] {
  const cuesFound: TextTrackCue[] = [];
  const firstCueInRange = getFirstCueIndexAfterTime(cues, start);
  if (firstCueInRange > -1) {
    for (let i = firstCueInRange, len = cues.length; i < len; i++) {
      const cue = cues[i];
      if (cue.startTime >= start && cue.endTime <= end) {
        cuesFound.push(cue);
      } else if (cue.startTime > end) {
        return cuesFound;
      }
    }
  }
  return cuesFound;
}