shaka-player
Version:
DASH/EME video player library
455 lines (395 loc) • 14.1 kB
JavaScript
/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.provide('shaka.cea.CeaDecoder');
goog.require('shaka.cea.Cea608DataChannel');
goog.require('shaka.cea.Cea708Service');
goog.require('shaka.cea.DtvccPacketBuilder');
goog.require('shaka.log');
goog.require('shaka.media.ClosedCaptionParser');
goog.require('shaka.util.DataViewReader');
goog.require('shaka.util.Error');
goog.requireType('shaka.cea.DtvccPacket');
/**
* CEA-X08 captions decoder.
* @implements {shaka.extern.ICaptionDecoder}
* @export
*/
shaka.cea.CeaDecoder = class {
/** */
constructor() {
/**
* An array of CEA-608 closed caption data extracted for decoding.
* @private {!Array<!shaka.cea.Cea608DataChannel.Cea608Packet>}
*/
this.cea608DataArray_ = [];
/**
* An array of CEA-708 closed caption data extracted for decoding.
* @private {!Array<!shaka.cea.Cea708Service.Cea708Byte>}
*/
this.cea708DataArray_ = [];
/**
* A DTVCC Packet builder for CEA-708 data.
* @private {!shaka.cea.DtvccPacketBuilder}
*/
this.dtvccPacketBuilder_ = new shaka.cea.DtvccPacketBuilder();
/**
* Number of consecutive bad frames decoded on CEA-608.
* @private {number}
*/
this.badFrames_ = 0;
/**
* A map containing the stream for each mode.
* @private {!Map<string, !shaka.cea.Cea608DataChannel>}
*/
this.cea608ModeToStream_ = new Map([
['CC1', new shaka.cea.Cea608DataChannel(0, 0)], // F1 + C1 -> CC1
['CC2', new shaka.cea.Cea608DataChannel(0, 1)], // F1 + C2 -> CC2
['CC3', new shaka.cea.Cea608DataChannel(1, 0)], // F2 + C1 -> CC3
['CC4', new shaka.cea.Cea608DataChannel(1, 1)], // F2 + C2 -> CC4
]);
/**
* The current channel that is active on CEA-608 field 1.
* @private {number}
*/
this.currentField1Channel_ = 0;
/**
* The current channel that is active on CEA-608 field 2.
* @private {number}
*/
this.currentField2Channel_ = 0;
/**
* Map of service number to CEA-708 services, initially empty. Since there
* can be up to 63 services, they are created dynamically only when needed.
* @private {!Map<number, shaka.cea.Cea708Service>}
*/
this.serviceNumberToService_ = new Map();
/**
* @private {boolean}
*/
this.waitingForFirstPacket_ = true;
/**
* Set used to track available streams.
* @private {!Set<string>}
*/
this.streams_ = new Set();
this.reset();
}
/**
* Clears the decoder.
* @override
*/
clear() {
shaka.log.debug('Clearing CEA decoder');
this.badFrames_ = 0;
this.cea608DataArray_ = [];
this.cea708DataArray_ = [];
this.dtvccPacketBuilder_.clear();
this.reset();
// Clear all the CEA-708 services.
for (const service of this.serviceNumberToService_.values()) {
service.clear();
}
}
/**
* Resets the decoder.
*/
reset() {
shaka.log.debug('Resetting CEA decoder');
this.currentField1Channel_ = 0;
this.currentField2Channel_ = 0;
for (const stream of this.cea608ModeToStream_.values()) {
stream.reset();
}
this.waitingForFirstPacket_ = true;
}
/**
* Extracts closed caption bytes from CEA-X08 packets from the stream based on
* ANSI/SCTE 128 and A/53, Part 4.
* @override
*/
extract(userDataSeiMessage, pts) {
if (this.waitingForFirstPacket_) {
shaka.log.debug('Setting first pts value to', pts);
for (const stream of this.cea608ModeToStream_.values()) {
stream.firstPts(pts);
}
this.waitingForFirstPacket_ = false;
}
const reader = new shaka.util.DataViewReader(
userDataSeiMessage, shaka.util.DataViewReader.Endianness.BIG_ENDIAN);
if (reader.getLength() < shaka.cea.CeaDecoder.MIN_LENGTH) {
return;
}
if (reader.readUint8() !== shaka.cea.CeaDecoder.USA_COUNTRY_CODE) {
return;
}
if (reader.readUint16() !== shaka.cea.CeaDecoder.ATSC_PROVIDER_CODE) {
return;
}
if (reader.readUint32() !== shaka.cea.CeaDecoder.ATSC1_USER_IDENTIFIER) {
return;
}
// user_data_type_code: 0x03 - cc_data()
if (reader.readUint8() !== 0x03) {
return;
}
// 1 bit reserved
// 1 bit process_cc_data_flag
// 1 bit zero_bit
// 5 bits cc_count
const captionData = reader.readUint8();
// If process_cc_data_flag is not set, do not process this data.
if ((captionData & 0x40) === 0) {
return;
}
const count = captionData & 0x1f;
// 8 bits reserved
reader.skip(1);
for (let i = 0; i < count; i++) {
const cc = reader.readUint8();
// When ccValid is 0, the next two bytes should be discarded.
const ccValid = (cc & 0x04) >> 2;
const ccData1 = reader.readUint8();
const ccData2 = reader.readUint8();
if (ccValid) {
const ccType = cc & 0x03;
// Send the packet to the appropriate data array (CEA-608 or CEA-708).
if (ccType === shaka.cea.CeaDecoder.NTSC_CC_FIELD_1 ||
ccType === shaka.cea.CeaDecoder.NTSC_CC_FIELD_2) {
// CEA-608 NTSC (Line 21) Data.
this.cea608DataArray_.push({
pts,
type: ccType,
ccData1,
ccData2,
order: this.cea608DataArray_.length,
});
} else {
// CEA-708 DTVCC Data.
this.cea708DataArray_.push({
pts,
type: ccType,
value: ccData1,
order: this.cea708DataArray_.length,
});
// The second byte should always be labelled as DTVCC packet data.
// Even if this pair was a DTVCC packet start, only the first byte
// contains header info, and the second byte is just packet data.
this.cea708DataArray_.push({
pts,
type: shaka.cea.DtvccPacketBuilder.DTVCC_PACKET_DATA,
value: ccData2,
order: this.cea708DataArray_.length,
});
}
}
}
}
/**
* Decodes extracted closed caption data.
* @override
*/
decode() {
/** @type {!Array<!shaka.extern.ICaptionDecoder.ClosedCaption>} */
const parsedClosedCaptions = [];
// In some versions of Chrome, and other browsers, the default sorting
// algorithm isn't stable. This comparator sorts on presentation
// timestamp, and breaks ties on receive order (position in array).
const stableComparator =
(p1, p2) => (p1.pts - p2.pts) || (p1.order - p2.order);
this.cea608DataArray_.sort(stableComparator);
this.cea708DataArray_.sort(stableComparator);
// CEA-608 packets are just byte pairs. Decode all of them.
for (const cea608Packet of this.cea608DataArray_) {
const parsedClosedCaption = this.decodeCea608_(cea608Packet);
if (parsedClosedCaption) {
parsedClosedCaptions.push(parsedClosedCaption);
}
}
// CEA-708 packets are DTVCC packets composed of many byte pairs. Add all
// byte pairs to the packet builder, and process + clear any ready packets.
for (const cea708Byte of this.cea708DataArray_) {
this.dtvccPacketBuilder_.addByte(cea708Byte);
}
const dtvccPackets = this.dtvccPacketBuilder_.getBuiltPackets();
for (const dtvccPacket of dtvccPackets) {
const closedCaptions = this.decodeCea708_(dtvccPacket);
parsedClosedCaptions.push(...closedCaptions);
}
// Clear all processed data.
this.dtvccPacketBuilder_.clearBuiltPackets();
this.cea608DataArray_ = [];
this.cea708DataArray_ = [];
return parsedClosedCaptions;
}
/**
* Decodes a CEA-608 closed caption packet based on ANSI/CEA-608.
* @param {shaka.cea.Cea608DataChannel.Cea608Packet} ccPacket
* @return {?shaka.extern.ICaptionDecoder.ClosedCaption}
* @private
*/
decodeCea608_(ccPacket) {
const fieldNum = ccPacket.type;
// If this packet is a control code, then it also sets the channel.
// For control codes, cc_data_1 has the form |P|0|0|1|C|X|X|X|.
// "C" is the channel bit. It indicates whether to set C2 active.
if (shaka.cea.Cea608DataChannel.isControlCode(ccPacket.ccData1)) {
const channelNum = (ccPacket.ccData1 >> 3) & 0x01; // Get channel bit.
// Change the stream based on the field, and the new channel
if (fieldNum === 0) {
this.currentField1Channel_ = channelNum;
} else {
this.currentField2Channel_ = channelNum;
}
}
// Get the correct stream for this caption packet (CC1, ..., CC4)
const selectedChannel = fieldNum ?
this.currentField2Channel_ : this.currentField1Channel_;
const selectedMode = `CC${((fieldNum << 1) | selectedChannel) + 1}`;
const selectedStream = this.cea608ModeToStream_.get(selectedMode);
// Check for bad frames (bad pairs). This can be two 0xff, two 0x00, or any
// byte of even parity. ccData1 and ccData2 should be uint8 of odd parity.
if ((ccPacket.ccData1 === 0xff && ccPacket.ccData2 === 0xff) ||
(!ccPacket.ccData1 && !ccPacket.ccData2) ||
!this.isOddParity_(ccPacket.ccData1) ||
!this.isOddParity_(ccPacket.ccData2)) {
// Per CEA-608-B C.21, reset the memory after 45 consecutive bad frames.
if (++this.badFrames_ >= 45) {
this.reset();
}
return null;
}
this.badFrames_ = 0;
// Remove the MSB (parity bit).
ccPacket.ccData1 &= 0x7f;
ccPacket.ccData2 &= 0x7f;
// Ignore XDS
if (shaka.cea.Cea608DataChannel.isXdsControlCode(ccPacket.ccData1)) {
return null;
}
// Check for empty captions and skip them.
if (!ccPacket.ccData1 && !ccPacket.ccData2) {
return null;
}
// Process the clean CC data pair.
let parsedClosedCaption = null;
if (shaka.cea.Cea608DataChannel.isControlCode(ccPacket.ccData1)) {
this.streams_.add(selectedMode);
parsedClosedCaption = selectedStream.handleControlCode(ccPacket);
} else {
// Handle as a Basic North American Character.
selectedStream.handleBasicNorthAmericanChar(
ccPacket.ccData1, ccPacket.ccData2);
}
return parsedClosedCaption;
}
/**
* Decodes a CEA-708 DTVCC packet based on ANSI/CTA-708-E.
* @param {shaka.cea.DtvccPacket} dtvccPacket
* @return {!Array<!shaka.extern.ICaptionDecoder.ClosedCaption>}
* @private
*/
decodeCea708_(dtvccPacket) {
const parsedClosedCaptions = [];
try {
while (dtvccPacket.hasMoreData()) {
// Process a service block.
const serviceBlockHeader = dtvccPacket.readByte().value;
// First 3 bits are service number, next 5 are block size,
// representing the number of bytes coming in this block
// (excluding a possible extended service block header byte)
let serviceNumber = (serviceBlockHeader & 0xe0) >> 5;
const blockSize = serviceBlockHeader & 0x1f;
if (serviceNumber === /* 0b111 */ 0x07 && blockSize != 0) {
// 2 bits null padding, 6 bits extended service number
const extendedServiceBlockHeader = dtvccPacket.readByte().value;
serviceNumber = extendedServiceBlockHeader & 0x3f;
}
// As per CEA-708-E, service number 0 is invalid, and should be ignored.
if (serviceNumber != 0) {
this.streams_.add('svc'+ serviceNumber);
// If the service doesn't already exist, create it.
if (!this.serviceNumberToService_.has(serviceNumber)) {
const service = new shaka.cea.Cea708Service(serviceNumber);
this.serviceNumberToService_.set(serviceNumber, service);
}
const service = this.serviceNumberToService_.get(serviceNumber);
// Process all control codes.
const startPos = dtvccPacket.getPosition();
// Execute this loop `blockSize` times, to decode the control codes.
while (dtvccPacket.getPosition() - startPos < blockSize) {
const closedCaptions = service.handleCea708ControlCode(dtvccPacket);
parsedClosedCaptions.push(...closedCaptions);
} // position < end of block
} // serviceNumber != 0
} // hasMoreData
} catch (error) {
if (error instanceof shaka.util.Error &&
error.code === shaka.util.Error.Code.BUFFER_READ_OUT_OF_BOUNDS) {
shaka.log.warnOnce('CEA708_INVALID_DATA',
'Buffer read out of bounds / invalid CEA-708 Data.');
} else {
// This is an unexpected error, and should be rethrown.
throw error;
}
}
return parsedClosedCaptions;
}
/**
* Checks if a byte has odd parity (Odd number of 1s in binary).
* @param {number} byte
* @return {boolean} True if the byte has odd parity.
* @private
*/
isOddParity_(byte) {
let parity = 0;
while (byte) {
parity ^= (byte & 1); // toggle parity if low bit is 1
byte >>= 1; // shift away the low bit
}
return parity === 1;
}
/**
* Returns the streams that the CEA decoder found.
*
* @override
*/
getStreams() {
return Array.from(this.streams_);
}
};
/**
* itu_t_35_provider_code for ATSC user_data
* @private @const {number}
*/
shaka.cea.CeaDecoder.ATSC_PROVIDER_CODE = 0x0031;
/**
* When provider is ATSC user data, the ATSC_user_identifier code
* for ATSC1_data is "GA94" (0x47413934)
* @private @const {number}
*/
shaka.cea.CeaDecoder.ATSC1_USER_IDENTIFIER = 0x47413934;
/**
* @private @const {number}
*/
shaka.cea.CeaDecoder.NTSC_CC_FIELD_1 = 0;
/**
* @private @const {number}
*/
shaka.cea.CeaDecoder.NTSC_CC_FIELD_2 = 1;
/**
* 0xB5 is USA's code (Rec. ITU-T T.35)
* @private @const {number}
*/
shaka.cea.CeaDecoder.USA_COUNTRY_CODE = 0xb5;
/**
* Caption packet min length
* Country Code + ATSC_PROVIDER_CODE + ATSC_1_USER_IDENTIFIER + USER_DATA_TYPE
* @private @const {number}
*/
shaka.cea.CeaDecoder.MIN_LENGTH = 8;
shaka.media.ClosedCaptionParser.registerDecoder(
() => new shaka.cea.CeaDecoder());