src/utils/cues.ts

import { fixLineBreaks } from './vttparser';
import type { CaptionScreen, Row } from './cea-608-parser';
import { generateCueId } from './webvtt-parser';
import { addCueToTrack } from './texttrack-utils';
 
const WHITESPACE_CHAR = /\s/;
 
export interface CuesInterface {
  newCue(
    track: TextTrack | null,
    startTime: number,
    endTime: number,
    captionScreen: CaptionScreen
  ): VTTCue[];
}
 
export function newCue(
  track: TextTrack | null,
  startTime: number,
  endTime: number,
  captionScreen: CaptionScreen
): VTTCue[] {
  const result: VTTCue[] = [];
  let row: Row;
  // the type data states this is VTTCue, but it can potentially be a TextTrackCue on old browsers
  let cue: VTTCue;
  let indenting: boolean;
  let indent: number;
  let text: string;
  const Cue = (self.VTTCue || self.TextTrackCue) as any;
 
  for (let r = 0; r < captionScreen.rows.length; r++) {
    row = captionScreen.rows[r];
    indenting = true;
    indent = 0;
    text = '';
 
    if (!row.isEmpty()) {
      for (let c = 0; c < row.chars.length; c++) {
        if (WHITESPACE_CHAR.test(row.chars[c].uchar) && indenting) {
          indent++;
        } else {
          text += row.chars[c].uchar;
          indenting = false;
        }
      }
      // To be used for cleaning-up orphaned roll-up captions
      row.cueStartTime = startTime;
 
      // Give a slight bump to the endTime if it's equal to startTime to avoid a SyntaxError in IE
      if (startTime === endTime) {
        endTime += 0.0001;
      }
 
      if (indent >= 16) {
        indent--;
      } else {
        indent++;
      }
 
      const cueText = fixLineBreaks(text.trim());
      const id = generateCueId(startTime, endTime, cueText);
 
      // If this cue already exists in the track do not push it
      if (!track || !track.cues || !track.cues.getCueById(id)) {
        cue = new Cue(startTime, endTime, cueText);
        cue.id = id;
        cue.line = r + 1;
        cue.align = 'left';
        // Clamp the position between 10 and 80 percent (CEA-608 PAC indent code)
        // https://dvcs.w3.org/hg/text-tracks/raw-file/default/608toVTT/608toVTT.html#positioning-in-cea-608
        // Firefox throws an exception and captions break with out of bounds 0-100 values
        cue.position = 10 + Math.min(80, Math.floor((indent * 8) / 32) * 10);
        result.push(cue);
      }
    }
  }
  if (track && result.length) {
    // Sort bottom cues in reverse order so that they render in line order when overlapping in Chrome
    result.sort((cueA, cueB) => {
      if (cueA.line === 'auto' || cueB.line === 'auto') {
        return 0;
      }
      if (cueA.line > 8 && cueB.line > 8) {
        return cueB.line - cueA.line;
      }
      return cueA.line - cueB.line;
    });
    result.forEach((cue) => addCueToTrack(track, cue));
  }
  return result;
}