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.Mp4CeaParser');
  12. goog.require('shaka.util.BufferUtils');
  13. goog.requireType('shaka.cea.ICaptionDecoder');
  14. goog.requireType('shaka.cea.ICeaParser');
  17. /**
  18.  * The IClosedCaptionParser defines the interface to provide all operations for
  19.  * parsing the closed captions embedded in Dash videos streams.
  20.  * TODO: Remove this interface and move method definitions
  21.  * directly to ClosedCaptonParser.
  22.  * @interface
  23.  */
  24. shaka.media.IClosedCaptionParser = class {
  25.   /**
  26.    * Initialize the caption parser. This should be called only once.
  27.    * @param {BufferSource} initSegment
  28.    */
  29.   init(initSegment) {}
  31.   /**
  32.    * Parses embedded CEA closed captions and interacts with the underlying
  33.    * CaptionStream, and calls the callback function when there are closed
  34.    * captions.
  35.    *
  36.    * @param {BufferSource} mediaFragment
  37.    * @return {!Array<!shaka.cea.ICaptionDecoder.ClosedCaption>}
  38.    * An array of parsed closed captions.
  39.    */
  40.   parseFrom(mediaFragment) {}
  42.   /**
  43.    * Resets the CaptionStream.
  44.    */
  45.   reset() {}
  46. };
  48. /**
  49.  * Closed Caption Parser provides all operations for parsing the closed captions
  50.  * embedded in Dash videos streams.
  51.  *
  52.  * @implements {shaka.media.IClosedCaptionParser}
  53.  * @final
  54.  */
  55. shaka.media.ClosedCaptionParser = class {
  56.   /** */
  57.   constructor() {
  58.     /**
  59.      * MP4 Parser to extract closed caption packets from H.264 video.
  60.      * @private {!shaka.cea.ICeaParser}
  61.      */
  62.     this.ceaParser_ = new shaka.cea.Mp4CeaParser();
  64.     /**
  65.      * Decoder for decoding CEA-X08 data from closed caption packets.
  66.      * @private {!shaka.cea.ICaptionDecoder}
  67.      */
  68.     this.ceaDecoder_ = new shaka.cea.CeaDecoder();
  69.   }
  71.   /**
  72.    * @override
  73.    */
  74.   init(initSegment) {
  75.     this.ceaParser_.init(initSegment);
  76.   }
  78.   /**
  79.    * @override
  80.    */
  81.   parseFrom(mediaFragment) {
  82.     // Parse the fragment.
  83.     const captionPackets = this.ceaParser_.parse(mediaFragment);
  85.     // Extract the caption packets for decoding.
  86.     for (const captionPacket of captionPackets) {
  87.       const uint8ArrayData =
  88.           shaka.util.BufferUtils.toUint8(captionPacket.packet);
  89.       if (uint8ArrayData.length > 0) {
  90.         this.ceaDecoder_.extract(uint8ArrayData, captionPacket.pts);
  91.       }
  92.     }
  94.     // Decode and return the parsed captions.
  95.     return this.ceaDecoder_.decode();
  96.   }
  98.   /**
  99.    * @override
  100.    */
  101.   reset() {
  102.     this.ceaDecoder_.clear();
  103.   }
  104. };