Source: lib/cea/cea_decoder.js

  1. /*! @license
  2.  * Shaka Player
  3.  * Copyright 2016 Google LLC
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  */
  7. goog.provide('shaka.cea.CeaDecoder');
  9. goog.require('shaka.cea.Cea608DataChannel');
  10. goog.require('shaka.cea.Cea708Service');
  11. goog.require('shaka.cea.DtvccPacketBuilder');
  12. goog.require('shaka.log');
  13. goog.require('shaka.media.ClosedCaptionParser');
  14. goog.require('shaka.util.DataViewReader');
  15. goog.require('shaka.util.Error');
  16. goog.requireType('shaka.cea.DtvccPacket');
  19. /**
  20.  * CEA-X08 captions decoder.
  21.  * @implements {shaka.extern.ICaptionDecoder}
  22.  * @export
  23.  */
  24. shaka.cea.CeaDecoder = class {
  25.   /** */
  26.   constructor() {
  27.     /**
  28.      * An array of CEA-608 closed caption data extracted for decoding.
  29.      * @private {!Array<!shaka.cea.Cea608DataChannel.Cea608Packet>}
  30.      */
  31.     this.cea608DataArray_ = [];
  33.     /**
  34.      * An array of CEA-708 closed caption data extracted for decoding.
  35.      * @private {!Array<!shaka.cea.Cea708Service.Cea708Byte>}
  36.      */
  37.     this.cea708DataArray_ = [];
  39.     /**
  40.      * A DTVCC Packet builder for CEA-708 data.
  41.      * @private {!shaka.cea.DtvccPacketBuilder}
  42.      */
  43.     this.dtvccPacketBuilder_ = new shaka.cea.DtvccPacketBuilder();
  45.     /**
  46.      * Number of consecutive bad frames decoded on CEA-608.
  47.      * @private {number}
  48.      */
  49.     this.badFrames_ = 0;
  51.     /**
  52.      * A map containing the stream for each mode.
  53.      * @private {!Map<string, !shaka.cea.Cea608DataChannel>}
  54.      */
  55.     this.cea608ModeToStream_ = new Map([
  56.       ['CC1', new shaka.cea.Cea608DataChannel(0, 0)], // F1 + C1 -> CC1
  57.       ['CC2', new shaka.cea.Cea608DataChannel(0, 1)], // F1 + C2 -> CC2
  58.       ['CC3', new shaka.cea.Cea608DataChannel(1, 0)], // F2 + C1 -> CC3
  59.       ['CC4', new shaka.cea.Cea608DataChannel(1, 1)], // F2 + C2 -> CC4
  60.     ]);
  62.     /**
  63.      * The current channel that is active on CEA-608 field 1.
  64.      * @private {number}
  65.      */
  66.     this.currentField1Channel_ = 0;
  68.     /**
  69.      * The current channel that is active on CEA-608 field 2.
  70.      * @private {number}
  71.      */
  72.     this.currentField2Channel_ = 0;
  74.     /**
  75.      * Map of service number to CEA-708 services, initially empty. Since there
  76.      * can be up to 63 services, they are created dynamically only when needed.
  77.      * @private {!Map<number, shaka.cea.Cea708Service>}
  78.      */
  79.     this.serviceNumberToService_ = new Map();
  81.     /**
  82.      * @private {boolean}
  83.      */
  84.     this.waitingForFirstPacket_ = true;
  86.     this.reset();
  87.   }
  89.   /**
  90.    * Clears the decoder.
  91.    * @override
  92.    */
  93.   clear() {
  94.     this.badFrames_ = 0;
  95.     this.cea608DataArray_ = [];
  96.     this.cea708DataArray_ = [];
  97.     this.dtvccPacketBuilder_.clear();
  98.     this.reset();
  100.     // Clear all the CEA-708 services.
  101.     for (const service of this.serviceNumberToService_.values()) {
  102.       service.clear();
  103.     }
  104.   }
  106.   /**
  107.    * Resets the decoder.
  108.    */
  109.   reset() {
  110.     this.currentField1Channel_ = 0;
  111.     this.currentField2Channel_ = 0;
  112.     for (const stream of this.cea608ModeToStream_.values()) {
  113.       stream.reset();
  114.     }
  115.     this.waitingForFirstPacket_ = true;
  116.   }
  118.   /**
  119.    * Extracts closed caption bytes from CEA-X08 packets from the stream based on
  120.    * ANSI/SCTE 128 and A/53, Part 4.
  121.    * @override
  122.    */
  123.   extract(userDataSeiMessage, pts) {
  124.     if (this.waitingForFirstPacket_) {
  125.       for (const stream of this.cea608ModeToStream_.values()) {
  126.         stream.firstPts(pts);
  127.       }
  128.       this.waitingForFirstPacket_ = false;
  129.     }
  131.     const reader = new shaka.util.DataViewReader(
  132.         userDataSeiMessage, shaka.util.DataViewReader.Endianness.BIG_ENDIAN);
  134.     if (reader.readUint8() !== shaka.cea.CeaDecoder.USA_COUNTRY_CODE) {
  135.       return;
  136.     }
  137.     if (reader.readUint16() !== shaka.cea.CeaDecoder.ATSC_PROVIDER_CODE) {
  138.       return;
  139.     }
  140.     if (reader.readUint32() !== shaka.cea.CeaDecoder.ATSC1_USER_IDENTIFIER) {
  141.       return;
  142.     }
  144.     // user_data_type_code: 0x03 - cc_data()
  145.     if (reader.readUint8() !== 0x03) {
  146.       return;
  147.     }
  149.     // 1 bit reserved
  150.     // 1 bit process_cc_data_flag
  151.     // 1 bit zero_bit
  152.     // 5 bits cc_count
  153.     const captionData = reader.readUint8();
  154.     // If process_cc_data_flag is not set, do not process this data.
  155.     if ((captionData & 0x40) === 0) {
  156.       return;
  157.     }
  159.     const count = captionData & 0x1f;
  161.     // 8 bits reserved
  162.     reader.skip(1);
  164.     for (let i = 0; i < count; i++) {
  165.       const cc = reader.readUint8();
  166.       // When ccValid is 0, the next two bytes should be discarded.
  167.       const ccValid = (cc & 0x04) >> 2;
  168.       const ccData1 = reader.readUint8();
  169.       const ccData2 = reader.readUint8();
  171.       if (ccValid) {
  172.         const ccType = cc & 0x03;
  173.         // Send the packet to the appropriate data array (CEA-608 or CEA-708).
  174.         if (ccType === shaka.cea.CeaDecoder.NTSC_CC_FIELD_1 ||
  175.             ccType === shaka.cea.CeaDecoder.NTSC_CC_FIELD_2) {
  176.           // CEA-608 NTSC (Line 21) Data.
  177.           this.cea608DataArray_.push({
  178.             pts,
  179.             type: ccType,
  180.             ccData1,
  181.             ccData2,
  182.             order: this.cea608DataArray_.length,
  183.           });
  184.         } else {
  185.           // CEA-708 DTVCC Data.
  186.           this.cea708DataArray_.push({
  187.             pts,
  188.             type: ccType,
  189.             value: ccData1,
  190.             order: this.cea708DataArray_.length,
  191.           });
  193.           // The second byte should always be labelled as DTVCC packet data.
  194.           // Even if this pair was a DTVCC packet start, only the first byte
  195.           // contains header info, and the second byte is just packet data.
  196.           this.cea708DataArray_.push({
  197.             pts,
  198.             type: shaka.cea.DtvccPacketBuilder.DTVCC_PACKET_DATA,
  199.             value: ccData2,
  200.             order: this.cea708DataArray_.length,
  201.           });
  202.         }
  203.       }
  204.     }
  205.   }
  207.   /**
  208.    * Decodes extracted closed caption data.
  209.    * @override
  210.    */
  211.   decode() {
  212.     /** @type {!Array.<!shaka.extern.ICaptionDecoder.ClosedCaption>} */
  213.     const parsedClosedCaptions = [];
  215.     // In some versions of Chrome, and other browsers, the default sorting
  216.     // algorithm isn't stable. This comparator sorts on presentation
  217.     // timestamp, and breaks ties on receive order (position in array).
  218.     const stableComparator =
  219.       (p1, p2) => (p1.pts - p2.pts) || (p1.order - p2.order);
  221.     this.cea608DataArray_.sort(stableComparator);
  222.     this.cea708DataArray_.sort(stableComparator);
  224.     // CEA-608 packets are just byte pairs. Decode all of them.
  225.     for (const cea608Packet of this.cea608DataArray_) {
  226.       const parsedClosedCaption = this.decodeCea608_(cea608Packet);
  227.       if (parsedClosedCaption) {
  228.         parsedClosedCaptions.push(parsedClosedCaption);
  229.       }
  230.     }
  232.     // CEA-708 packets are DTVCC packets composed of many byte pairs. Add all
  233.     // byte pairs to the packet builder, and process + clear any ready packets.
  234.     for (const cea708Byte of this.cea708DataArray_) {
  235.       this.dtvccPacketBuilder_.addByte(cea708Byte);
  236.     }
  237.     const dtvccPackets = this.dtvccPacketBuilder_.getBuiltPackets();
  238.     for (const dtvccPacket of dtvccPackets) {
  239.       const closedCaptions = this.decodeCea708_(dtvccPacket);
  240.       parsedClosedCaptions.push(...closedCaptions);
  241.     }
  243.     // Clear all processed data.
  244.     this.dtvccPacketBuilder_.clearBuiltPackets();
  245.     this.cea608DataArray_ = [];
  246.     this.cea708DataArray_ = [];
  248.     return parsedClosedCaptions;
  249.   }
  251.   /**
  252.    * Decodes a CEA-608 closed caption packet based on ANSI/CEA-608.
  253.    * @param {shaka.cea.Cea608DataChannel.Cea608Packet} ccPacket
  254.    * @return {?shaka.extern.ICaptionDecoder.ClosedCaption}
  255.    * @private
  256.    */
  257.   decodeCea608_(ccPacket) {
  258.     const fieldNum = ccPacket.type;
  260.     // If this packet is a control code, then it also sets the channel.
  261.     // For control codes, cc_data_1 has the form |P|0|0|1|C|X|X|X|.
  262.     // "C" is the channel bit. It indicates whether to set C2 active.
  263.     if (shaka.cea.Cea608DataChannel.isControlCode(ccPacket.ccData1)) {
  264.       const channelNum = (ccPacket.ccData1 >> 3) & 0x01; // Get channel bit.
  266.       // Change the stream based on the field, and the new channel
  267.       if (fieldNum === 0) {
  268.         this.currentField1Channel_ = channelNum;
  269.       } else {
  270.         this.currentField2Channel_ = channelNum;
  271.       }
  272.     }
  274.     // Get the correct stream for this caption packet (CC1, ..., CC4)
  275.     const selectedChannel = fieldNum ?
  276.         this.currentField2Channel_ : this.currentField1Channel_;
  277.     const selectedMode = `CC${(fieldNum << 1) | selectedChannel + 1}`;
  278.     const selectedStream = this.cea608ModeToStream_.get(selectedMode);
  280.     // Check for bad frames (bad pairs). This can be two 0xff, two 0x00, or any
  281.     // byte of even parity. ccData1 and ccData2 should be uint8 of odd parity.
  282.     if ((ccPacket.ccData1 === 0xff && ccPacket.ccData2 === 0xff) ||
  283.         (!ccPacket.ccData1 && !ccPacket.ccData2) ||
  284.         !this.isOddParity_(ccPacket.ccData1) ||
  285.         !this.isOddParity_(ccPacket.ccData2)) {
  286.       // Per CEA-608-B C.21, reset the memory after 45 consecutive bad frames.
  287.       if (++this.badFrames_ >= 45) {
  288.         this.reset();
  289.       }
  290.       return null;
  291.     }
  292.     this.badFrames_ = 0;
  294.     // Remove the MSB (parity bit).
  295.     ccPacket.ccData1 &= 0x7f;
  296.     ccPacket.ccData2 &= 0x7f;
  298.     // Check for empty captions and skip them.
  299.     if (!ccPacket.ccData1 && !ccPacket.ccData2) {
  300.       return null;
  301.     }
  303.     // Process the clean CC data pair.
  304.     let parsedClosedCaption = null;
  305.     if (shaka.cea.Cea608DataChannel.isControlCode(ccPacket.ccData1)) {
  306.       parsedClosedCaption = selectedStream.handleControlCode(ccPacket);
  307.     } else {
  308.       // Handle as a Basic North American Character.
  309.       selectedStream.handleBasicNorthAmericanChar(
  310.           ccPacket.ccData1, ccPacket.ccData2);
  311.     }
  313.     return parsedClosedCaption;
  314.   }
  316.   /**
  317.    * Decodes a CEA-708 DTVCC packet based on ANSI/CTA-708-E.
  318.    * @param {shaka.cea.DtvccPacket} dtvccPacket
  319.    * @return {!Array<!shaka.extern.ICaptionDecoder.ClosedCaption>}
  320.    * @private
  321.    */
  322.   decodeCea708_(dtvccPacket) {
  323.     const parsedClosedCaptions = [];
  324.     try {
  325.       while (dtvccPacket.hasMoreData()) {
  326.         // Process a service block.
  327.         const serviceBlockHeader = dtvccPacket.readByte().value;
  329.         // First 3 bits are service number, next 5 are block size,
  330.         // representing the number of bytes coming in this block
  331.         // (discluding a possible extended service block header byte)
  332.         let serviceNumber = (serviceBlockHeader & 0xe0) >> 5;
  333.         const blockSize = serviceBlockHeader & 0x1f;
  335.         if (serviceNumber === /* 0b111 */ 0x07 && blockSize != 0) {
  336.           // 2 bits null padding, 6 bits extended service number
  337.           const extendedServiceBlockHeader = dtvccPacket.readByte().value;
  338.           serviceNumber = extendedServiceBlockHeader & 0x3f;
  339.         }
  341.         // As per CEA-708-E, service number 0 is invalid, and should be ignored.
  342.         if (serviceNumber != 0) {
  343.           // If the service doesn't already exist, create it.
  344.           if (!this.serviceNumberToService_.has(serviceNumber)) {
  345.             const service = new shaka.cea.Cea708Service(serviceNumber);
  346.             this.serviceNumberToService_.set(serviceNumber, service);
  347.           }
  348.           const service = this.serviceNumberToService_.get(serviceNumber);
  350.           // Process all control codes.
  351.           const startPos = dtvccPacket.getPosition();
  353.           // Execute this loop `blockSize` times, to decode the control codes.
  354.           while (dtvccPacket.getPosition() - startPos < blockSize) {
  355.             const closedCaption = service.handleCea708ControlCode(dtvccPacket);
  356.             if (closedCaption) {
  357.               parsedClosedCaptions.push(closedCaption);
  358.             }
  359.           }  // position < end of block
  360.         }  // serviceNumber != 0
  361.       }  // hasMoreData
  362.     } catch (error) {
  363.       if (error instanceof shaka.util.Error &&
  364.       error.code === shaka.util.Error.Code.BUFFER_READ_OUT_OF_BOUNDS) {
  365.         shaka.log.warnOnce('CEA708_INVALID_DATA',
  366.             'Buffer read out of bounds / invalid CEA-708 Data.');
  367.       } else {
  368.         // This is an unexpected error, and should be rethrown.
  369.         throw error;
  370.       }
  371.     }
  372.     return parsedClosedCaptions;
  373.   }
  375.   /**
  376.    * Checks if a byte has odd parity (Odd number of 1s in binary).
  377.    * @param {number} byte
  378.    * @return {boolean} True if the byte has odd parity.
  379.    * @private
  380.    */
  381.   isOddParity_(byte) {
  382.     let parity = 0;
  383.     while (byte) {
  384.       parity ^= (byte & 1); // toggle parity if low bit is 1
  385.       byte >>= 1; // shift away the low bit
  386.     }
  387.     return parity === 1;
  388.   }
  389. };
  391. /**
  392.  * itu_t_35_provider_code for ATSC user_data
  393.  * @private @const {number}
  394.  */
  395. shaka.cea.CeaDecoder.ATSC_PROVIDER_CODE = 0x0031;
  397. /**
  398.  * When provider is ATSC user data, the ATSC_user_identifier code
  399.  * for ATSC1_data is "GA94" (0x47413934)
  400.  * @private @const {number}
  401.  */
  402. shaka.cea.CeaDecoder.ATSC1_USER_IDENTIFIER = 0x47413934;
  404. /**
  405.  * @private @const {number}
  406.  */
  407. shaka.cea.CeaDecoder.NTSC_CC_FIELD_1 = 0;
  409. /**
  410.  * @private @const {number}
  411.  */
  412. shaka.cea.CeaDecoder.NTSC_CC_FIELD_2 = 1;
  414. /**
  415.  * 0xB5 is USA's code (Rec. ITU-T T.35)
  416.  * @private @const {number}
  417.  */
  418. shaka.cea.CeaDecoder.USA_COUNTRY_CODE = 0xb5;
  420. shaka.media.ClosedCaptionParser.registerDecoder(
  421.     () => new shaka.cea.CeaDecoder());