Source: lib/text/simple_text_displayer.js

  1. /*! @license
  2.  * Shaka Player
  3.  * Copyright 2016 Google LLC
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  */
  7. /**
  8.  * @fileoverview
  9.  */
  11. goog.provide('shaka.text.SimpleTextDisplayer');
  13. goog.require('goog.asserts');
  14. goog.require('shaka.log');
  15. goog.require('shaka.text.Cue');
  16. goog.require('shaka.text.Utils');
  19. /**
  20.  * A text displayer plugin using the browser's native VTTCue interface.
  21.  *
  22.  * @implements {shaka.extern.TextDisplayer}
  23.  * @export
  24.  */
  25. shaka.text.SimpleTextDisplayer = class {
  26.   /**
  27.    * @param {HTMLMediaElement} video
  28.    * @param {string} label
  29.    */
  30.   constructor(video, label) {
  31.     /** @private {TextTrack} */
  32.     this.textTrack_ = null;
  34.     // TODO: Test that in all cases, the built-in CC controls in the video
  35.     // element are toggling our TextTrack.
  37.     // If the video element has TextTracks, disable them.  If we see one that
  38.     // was created by a previous instance of Shaka Player, reuse it.
  39.     for (const track of Array.from(video.textTracks)) {
  40.       // NOTE: There is no API available to remove a TextTrack from a video
  41.       // element.
  42.       track.mode = 'disabled';
  44.       if (track.label == label) {
  45.         this.textTrack_ = track;
  46.       }
  47.     }
  49.     if (!this.textTrack_) {
  50.       // As far as I can tell, there is no observable difference between setting
  51.       // kind to 'subtitles' or 'captions' when creating the TextTrack object.
  52.       // The individual text tracks from the manifest will still have their own
  53.       // kinds which can be displayed in the app's UI.
  54.       this.textTrack_ = video.addTextTrack('subtitles', label);
  55.     }
  56.     this.textTrack_.mode = 'hidden';
  57.   }
  60.   /**
  61.    * @override
  62.    * @export
  63.    */
  64.   configure(config) {
  65.     // Unused.
  66.   }
  68.   /**
  69.    * @override
  70.    * @export
  71.    */
  72.   remove(start, end) {
  73.     // Check that the displayer hasn't been destroyed.
  74.     if (!this.textTrack_) {
  75.       return false;
  76.     }
  78.     const removeInRange = (cue) => {
  79.       const inside = cue.startTime < end && cue.endTime > start;
  80.       return inside;
  81.     };
  83.     shaka.text.SimpleTextDisplayer.removeWhere_(this.textTrack_, removeInRange);
  85.     return true;
  86.   }
  88.   /**
  89.    * @override
  90.    * @export
  91.    */
  92.   append(cues) {
  93.     const flattenedCues = shaka.text.Utils.getCuesToFlatten(cues);
  95.     // Convert cues.
  96.     const textTrackCues = [];
  97.     const cuesInTextTrack = this.textTrack_.cues ?
  98.                             Array.from(this.textTrack_.cues) : [];
  100.     for (const inCue of flattenedCues) {
  101.       // When a VTT cue spans a segment boundary, the cue will be duplicated
  102.       // into two segments.
  103.       // To avoid displaying duplicate cues, if the current textTrack cues
  104.       // list already contains the cue, skip it.
  105.       const containsCue = cuesInTextTrack.some((cueInTextTrack) => {
  106.         if (cueInTextTrack.startTime == inCue.startTime &&
  107.             cueInTextTrack.endTime == inCue.endTime &&
  108.             cueInTextTrack.text == inCue.payload) {
  109.           return true;
  110.         }
  111.         return false;
  112.       });
  114.       if (!containsCue) {
  115.         const cue =
  116.             shaka.text.SimpleTextDisplayer.convertToTextTrackCue_(inCue);
  117.         if (cue) {
  118.           textTrackCues.push(cue);
  119.         }
  120.       }
  121.     }
  123.     // Sort the cues based on start/end times.  Make a copy of the array so
  124.     // we can get the index in the original ordering.  Out of order cues are
  125.     // rejected by Edge.  See https://bit.ly/2K9VX3s
  126.     const sortedCues = textTrackCues.slice().sort((a, b) => {
  127.       if (a.startTime != b.startTime) {
  128.         return a.startTime - b.startTime;
  129.       } else if (a.endTime != b.endTime) {
  130.         return a.endTime - b.startTime;
  131.       } else {
  132.         // The browser will display cues with identical time ranges from the
  133.         // bottom up.  Reversing the order of equal cues means the first one
  134.         // parsed will be at the top, as you would expect.
  135.         // See https://github.com/shaka-project/shaka-player/issues/848 for
  136.         // more info.
  137.         // However, this ordering behavior is part of VTTCue's "line" field.
  138.         // Some platforms don't have a real VTTCue and use a polyfill instead.
  139.         // When VTTCue is polyfilled or does not support "line", we should _not_
  140.         // reverse the order.  This occurs on legacy Edge.
  141.         // eslint-disable-next-line no-restricted-syntax
  142.         if ('line' in VTTCue.prototype) {
  143.           // Native VTTCue
  144.           return textTrackCues.indexOf(b) - textTrackCues.indexOf(a);
  145.         } else {
  146.           // Polyfilled VTTCue
  147.           return textTrackCues.indexOf(a) - textTrackCues.indexOf(b);
  148.         }
  149.       }
  150.     });
  152.     for (const cue of sortedCues) {
  153.       this.textTrack_.addCue(cue);
  154.     }
  155.   }
  157.   /**
  158.    * @override
  159.    * @export
  160.    */
  161.   destroy() {
  162.     if (this.textTrack_) {
  163.       const removeIt = (cue) => true;
  164.       shaka.text.SimpleTextDisplayer.removeWhere_(this.textTrack_, removeIt);
  166.       // NOTE: There is no API available to remove a TextTrack from a video
  167.       // element.
  168.       this.textTrack_.mode = 'disabled';
  169.     }
  171.     this.textTrack_ = null;
  172.     return Promise.resolve();
  173.   }
  175.   /**
  176.    * @override
  177.    * @export
  178.    */
  179.   isTextVisible() {
  180.     return this.textTrack_.mode == 'showing';
  181.   }
  183.   /**
  184.    * @override
  185.    * @export
  186.    */
  187.   setTextVisibility(on) {
  188.     this.textTrack_.mode = on ? 'showing' : 'hidden';
  189.   }
  191.   /**
  192.    * @param {!shaka.text.Cue} shakaCue
  193.    * @return {TextTrackCue}
  194.    * @private
  195.    */
  196.   static convertToTextTrackCue_(shakaCue) {
  197.     if (shakaCue.startTime >= shakaCue.endTime) {
  198.       // Edge will throw in this case.
  199.       // See issue #501
  200.       shaka.log.warning('Invalid cue times: ' + shakaCue.startTime +
  201.                         ' - ' + shakaCue.endTime);
  202.       return null;
  203.     }
  205.     const Cue = shaka.text.Cue;
  206.     /** @type {VTTCue} */
  207.     const vttCue = new VTTCue(
  208.         shakaCue.startTime,
  209.         shakaCue.endTime,
  210.         shakaCue.payload);
  212.     // NOTE: positionAlign and lineAlign settings are not supported by Chrome
  213.     // at the moment, so setting them will have no effect.
  214.     // The bug on chromium to implement them:
  215.     // https://bugs.chromium.org/p/chromium/issues/detail?id=633690
  217.     vttCue.lineAlign = shakaCue.lineAlign;
  218.     vttCue.positionAlign = shakaCue.positionAlign;
  219.     if (shakaCue.size) {
  220.       vttCue.size = shakaCue.size;
  221.     }
  223.     try {
  224.       // Safari 10 seems to throw on align='center'.
  225.       vttCue.align = shakaCue.textAlign;
  226.     } catch (exception) {}
  228.     if (shakaCue.textAlign == 'center' && vttCue.align != 'center') {
  229.       // We want vttCue.position = 'auto'. By default, |position| is set to
  230.       // "auto". If we set it to "auto" safari will throw an exception, so we
  231.       // must rely on the default value.
  232.       vttCue.align = 'middle';
  233.     }
  235.     if (shakaCue.writingMode ==
  236.             Cue.writingMode.VERTICAL_LEFT_TO_RIGHT) {
  237.       vttCue.vertical = 'lr';
  238.     } else if (shakaCue.writingMode ==
  239.              Cue.writingMode.VERTICAL_RIGHT_TO_LEFT) {
  240.       vttCue.vertical = 'rl';
  241.     }
  243.     // snapToLines flag is true by default
  244.     if (shakaCue.lineInterpretation == Cue.lineInterpretation.PERCENTAGE) {
  245.       vttCue.snapToLines = false;
  246.     }
  248.     if (shakaCue.line != null) {
  249.       vttCue.line = shakaCue.line;
  250.     }
  252.     if (shakaCue.position != null) {
  253.       vttCue.position = shakaCue.position;
  254.     }
  256.     return vttCue;
  257.   }
  259.   /**
  260.    * Iterate over all the cues in a text track and remove all those for which
  261.    * |predicate(cue)| returns true.
  262.    *
  263.    * @param {!TextTrack} track
  264.    * @param {function(!TextTrackCue):boolean} predicate
  265.    * @private
  266.    */
  267.   static removeWhere_(track, predicate) {
  268.     // Since |track.cues| can be null if |track.mode| is "disabled", force it to
  269.     // something other than "disabled".
  270.     //
  271.     // If the track is already showing, then we should keep it as showing. But
  272.     // if it something else, we will use hidden so that we don't "flash" cues on
  273.     // the screen.
  274.     const oldState = track.mode;
  275.     const tempState = oldState == 'showing' ? 'showing' : 'hidden';
  277.     track.mode = tempState;
  279.     goog.asserts.assert(
  280.         track.cues,
  281.         'Cues should be accessible when mode is set to "' + tempState + '".');
  283.     // Create a copy of the list to avoid errors while iterating.
  284.     for (const cue of Array.from(track.cues)) {
  285.       if (cue && predicate(cue)) {
  286.         track.removeCue(cue);
  287.       }
  288.     }
  290.     track.mode = oldState;
  291.   }
  292. };