Source: lib/media/closed_caption_parser.js

  1. /*! @license
  2.  * Shaka Player
  3.  * Copyright 2016 Google LLC
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  */
  7. goog.provide('shaka.media.ClosedCaptionParser');
  8. goog.provide('shaka.media.IClosedCaptionParser');
  10. goog.require('shaka.cea.CeaDecoder');
  11. goog.require('shaka.cea.DummyCeaParser');
  12. goog.require('shaka.cea.Mp4CeaParser');
  13. goog.require('shaka.util.BufferUtils');
  14. goog.requireType('shaka.cea.ICaptionDecoder');
  15. goog.requireType('shaka.cea.ICeaParser');
  18. /**
  19.  * The IClosedCaptionParser defines the interface to provide all operations for
  20.  * parsing the closed captions embedded in Dash videos streams.
  21.  * TODO: Remove this interface and move method definitions
  22.  * directly to ClosedCaptonParser.
  23.  * @interface
  24.  */
  25. shaka.media.IClosedCaptionParser = class {
  26.   /**
  27.    * Initialize the caption parser. This should be called only once.
  28.    * @param {BufferSource} initSegment
  29.    */
  30.   init(initSegment) {}
  32.   /**
  33.    * Parses embedded CEA closed captions and interacts with the underlying
  34.    * CaptionStream, and calls the callback function when there are closed
  35.    * captions.
  36.    *
  37.    * @param {BufferSource} mediaFragment
  38.    * @return {!Array<!shaka.cea.ICaptionDecoder.ClosedCaption>}
  39.    * An array of parsed closed captions.
  40.    */
  41.   parseFrom(mediaFragment) {}
  43.   /**
  44.    * Resets the CaptionStream.
  45.    */
  46.   reset() {}
  47. };
  49. /**
  50.  * Closed Caption Parser provides all operations for parsing the closed captions
  51.  * embedded in Dash videos streams.
  52.  *
  53.  * @implements {shaka.media.IClosedCaptionParser}
  54.  * @final
  55.  */
  56. shaka.media.ClosedCaptionParser = class {
  57.   /** */
  58.   constructor(mimeType) {
  59.     /** @private {!shaka.cea.ICeaParser} */
  60.     this.ceaParser_ = new shaka.cea.DummyCeaParser();
  62.     if (mimeType.includes('video/mp4')) {
  63.       // MP4 Parser to extract closed caption packets from H.264 video.
  64.       this.ceaParser_ = new shaka.cea.Mp4CeaParser();
  65.     }
  67.     /**
  68.      * Decoder for decoding CEA-X08 data from closed caption packets.
  69.      * @private {!shaka.cea.ICaptionDecoder}
  70.      */
  71.     this.ceaDecoder_ = new shaka.cea.CeaDecoder();
  72.   }
  74.   /**
  75.    * @override
  76.    */
  77.   init(initSegment) {
  78.     this.ceaParser_.init(initSegment);
  79.   }
  81.   /**
  82.    * @override
  83.    */
  84.   parseFrom(mediaFragment) {
  85.     // Parse the fragment.
  86.     const captionPackets = this.ceaParser_.parse(mediaFragment);
  88.     // Extract the caption packets for decoding.
  89.     for (const captionPacket of captionPackets) {
  90.       const uint8ArrayData =
  91.           shaka.util.BufferUtils.toUint8(captionPacket.packet);
  92.       if (uint8ArrayData.length > 0) {
  93.         this.ceaDecoder_.extract(uint8ArrayData, captionPacket.pts);
  94.       }
  95.     }
  97.     // Decode and return the parsed captions.
  98.     return this.ceaDecoder_.decode();
  99.   }
  101.   /**
  102.    * @override
  103.    */
  104.   reset() {
  105.     this.ceaDecoder_.clear();
  106.   }
  107. };