Source: lib/text/web_vtt_generator.js

  1. /*! @license
  2.  * Shaka Player
  3.  * Copyright 2016 Google LLC
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  */
  7. goog.provide('shaka.text.WebVttGenerator');
  9. goog.require('shaka.text.Cue');
  12. /**
  13.  * @summary Manage the conversion to WebVTT.
  14.  * @export
  15.  */
  16. shaka.text.WebVttGenerator = class {
  17.   /**
  18.    * @param {!Array.<!shaka.text.Cue>} cues
  19.    * @param {!Array.<!shaka.extern.AdCuePoint>} adCuePoints
  20.    * @return {string}
  21.    */
  22.   static convert(cues, adCuePoints) {
  23.     // Flatten nested cue payloads recursively.  If a cue has nested cues,
  24.     // their contents should be combined and replace the payload of the parent.
  25.     const flattenPayload = (cue) => {
  26.       // Handle styles (currently bold/italics/underline).
  27.       // TODO: add support for color rendering.
  28.       const openStyleTags = [];
  29.       const bold = cue.fontWeight >= shaka.text.Cue.fontWeight.BOLD;
  30.       const italics = cue.fontStyle == shaka.text.Cue.fontStyle.ITALIC;
  31.       const underline = cue.textDecoration.includes(
  32.           shaka.text.Cue.textDecoration.UNDERLINE);
  33.       if (bold) {
  34.         openStyleTags.push('b');
  35.       }
  36.       if (italics) {
  37.         openStyleTags.push('i');
  38.       }
  39.       if (underline) {
  40.         openStyleTags.push('u');
  41.       }
  43.       // Prefix opens tags, suffix closes tags in reverse order of opening.
  44.       const prefixStyleTags = openStyleTags.reduce((acc, tag) => {
  45.         return `${acc}<${tag}>`;
  46.       }, '');
  47.       const suffixStyleTags = openStyleTags.reduceRight((acc, tag) => {
  48.         return `${acc}</${tag}>`;
  49.       }, '');
  51.       if (cue.lineBreak) {
  52.         // This is a vertical lineBreak, so insert a newline.
  53.         return '\n';
  54.       } else if (cue.nestedCues.length) {
  55.         return cue.nestedCues.map(flattenPayload).join('');
  56.       } else {
  57.         // This is a real cue.
  58.         return prefixStyleTags + cue.payload + suffixStyleTags;
  59.       }
  60.     };
  62.     const webvttTimeString = (time) => {
  63.       let newTime = time;
  64.       for (const adCuePoint of adCuePoints) {
  65.         if (adCuePoint.end && adCuePoint.start < time) {
  66.           const offset = adCuePoint.end - adCuePoint.start;
  67.           newTime += offset;
  68.         }
  69.       }
  70.       const hours = Math.floor(newTime / 3600);
  71.       const minutes = Math.floor(newTime / 60 % 60);
  72.       const seconds = Math.floor(newTime % 60);
  73.       const milliseconds = Math.floor(newTime * 1000 % 1000);
  74.       return (hours < 10 ? '0' : '') + hours + ':' +
  75.           (minutes < 10 ? '0' : '') + minutes + ':' +
  76.           (seconds < 10 ? '0' : '') + seconds + '.' +
  77.           (milliseconds < 100 ? (milliseconds < 10 ? '00' : '0') : '') +
  78.           milliseconds;
  79.     };
  81.     // We don't want to modify the array or objects passed in, since we don't
  82.     // technically own them.  So we build a new array and replace certain items
  83.     // in it if they need to be flattened.
  84.     const flattenedCues = cues.map((cue) => {
  85.       if (cue.nestedCues.length) {
  86.         const flatCue = cue.clone();
  87.         flatCue.nestedCues = [];
  88.         flatCue.payload = flattenPayload(cue);
  89.         return flatCue;
  90.       } else {
  91.         return cue;
  92.       }
  93.     });
  95.     let webvttString = 'WEBVTT\n\n';
  96.     for (const cue of flattenedCues) {
  97.       const webvttSettings = (cue) => {
  98.         const settings = [];
  99.         const Cue = shaka.text.Cue;
  100.         switch (cue.textAlign) {
  101.           case Cue.textAlign.LEFT:
  102.             settings.push('align:left');
  103.             break;
  104.           case Cue.textAlign.RIGHT:
  105.             settings.push('align:right');
  106.             break;
  107.           case Cue.textAlign.CENTER:
  108.             settings.push('align:middle');
  109.             break;
  110.           case Cue.textAlign.START:
  111.             settings.push('align:start');
  112.             break;
  113.           case Cue.textAlign.END:
  114.             settings.push('align:end');
  115.             break;
  116.         }
  117.         switch (cue.writingMode) {
  118.           case Cue.writingMode.VERTICAL_LEFT_TO_RIGHT:
  119.             settings.push('vertical:lr');
  120.             break;
  121.           case Cue.writingMode.VERTICAL_RIGHT_TO_LEFT:
  122.             settings.push('vertical:rl');
  123.             break;
  124.         }
  126.         if (settings.length) {
  127.           return ' ' + settings.join(' ');
  128.         }
  129.         return '';
  130.       };
  131.       webvttString += webvttTimeString(cue.startTime) + ' --> ' +
  132.           webvttTimeString(cue.endTime) + webvttSettings(cue) + '\n';
  133.       webvttString += cue.payload + '\n\n';
  134.     }
  135.     return webvttString;
  136.   }
  137. };