jsmpeg/src/ts.js

JSMpeg.Demuxer.TS = (function(){ "use strict";

var TS = function(options) {
	this.bits = null;
	this.leftoverBytes = null;

	this.guessVideoFrameEnd = true;
	this.pidsToStreamIds = {};

	this.pesPacketInfo = {};
	this.startTime = 0;
	this.currentTime = 0;
};

TS.prototype.connect = function(streamId, destination) {
	this.pesPacketInfo[streamId] = {
		destination: destination,
		currentLength: 0,
		totalLength: 0,
		pts: 0,
		buffers: []
	};
};

TS.prototype.write = function(buffer) {
	if (this.leftoverBytes) {
		var totalLength = buffer.byteLength + this.leftoverBytes.byteLength;
		this.bits = new JSMpeg.BitBuffer(totalLength);
		this.bits.write([this.leftoverBytes, buffer]);
	}
	else {
		this.bits = new JSMpeg.BitBuffer(buffer);
	}

	while (this.bits.has(188 << 3) && this.parsePacket()) {}

	var leftoverCount = this.bits.byteLength - (this.bits.index >> 3);
	this.leftoverBytes = leftoverCount > 0
		? this.bits.bytes.subarray(this.bits.index >> 3)
		: null;
};

TS.prototype.parsePacket = function() {
	// Check if we're in sync with packet boundaries; attempt to resync if not.
	if (this.bits.read(8) !== 0x47) {
		if (!this.resync()) {
			// Couldn't resync; maybe next time...
			return false;
		}
	}

	var end = (this.bits.index >> 3) + 187;
	var transportError = this.bits.read(1),
		payloadStart = this.bits.read(1),
		transportPriority = this.bits.read(1),
		pid = this.bits.read(13),
		transportScrambling = this.bits.read(2),
		adaptationField = this.bits.read(2),
		continuityCounter = this.bits.read(4);


	// If this is the start of a new payload; signal the end of the previous
	// frame, if we didn't do so already.
	var streamId = this.pidsToStreamIds[pid];
	if (payloadStart && streamId) {
		var pi = this.pesPacketInfo[streamId];
		if (pi && pi.currentLength) {
			this.packetComplete(pi);
		}
	}

	// Extract current payload
	if (adaptationField & 0x1) {
		if ((adaptationField & 0x2)) {
			var adaptationFieldLength = this.bits.read(8);
			this.bits.skip(adaptationFieldLength << 3);
		}

		if (payloadStart && this.bits.nextBytesAreStartCode()) {
			this.bits.skip(24);
			streamId = this.bits.read(8);
			this.pidsToStreamIds[pid] = streamId;

			var packetLength = this.bits.read(16)
			this.bits.skip(8);
			var ptsDtsFlag = this.bits.read(2);
			this.bits.skip(6);
			var headerLength = this.bits.read(8);
			var payloadBeginIndex = this.bits.index + (headerLength << 3);
			
			var pi = this.pesPacketInfo[streamId];
			if (pi) {
				var pts = 0;
				if (ptsDtsFlag & 0x2) {
					// The Presentation Timestamp is encoded as 33(!) bit
					// integer, but has a "marker bit" inserted at weird places
					// in between, making the whole thing 5 bytes in size.
					// You can't make this shit up...
					this.bits.skip(4);
					var p32_30 = this.bits.read(3);
					this.bits.skip(1);
					var p29_15 = this.bits.read(15);
					this.bits.skip(1);
					var p14_0 = this.bits.read(15);
					this.bits.skip(1);

					// Can't use bit shifts here; we need 33 bits of precision,
					// so we're using JavaScript's double number type. Also
					// divide by the 90khz clock to get the pts in seconds.
					pts = (p32_30 * 1073741824 + p29_15 * 32768 + p14_0)/90000;
					
					this.currentTime = pts;
					if (this.startTime === -1) {
						this.startTime = pts;
					}
				}

				var payloadLength = packetLength 
					? packetLength - headerLength - 3
					: 0;
				this.packetStart(pi, pts, payloadLength);
			}

			// Skip the rest of the header without parsing it
			this.bits.index = payloadBeginIndex;
		}

		if (streamId) {
			// Attempt to detect if the PES packet is complete. For Audio (and
			// other) packets, we received a total packet length with the PES 
			// header, so we can check the current length.

			// For Video packets, we have to guess the end by detecting if this
			// TS packet was padded - there's no good reason to pad a TS packet 
			// in between, but it might just fit exactly. If this fails, we can
			// only wait for the next PES header for that stream.

			var pi = this.pesPacketInfo[streamId];
			if (pi) {
				var start = this.bits.index >> 3;
				var complete = this.packetAddData(pi, start, end);

				var hasPadding = !payloadStart && (adaptationField & 0x2);
				if (complete || (this.guessVideoFrameEnd && hasPadding)) {
					this.packetComplete(pi);	
				}
			}
		}
	}

	this.bits.index = end << 3;
	return true;
};

TS.prototype.resync = function() {
	// Check if we have enough data to attempt a resync. We need 5 full packets.
	if (!this.bits.has((188 * 6) << 3)) {
		return false;
	}

	var byteIndex = this.bits.index >> 3;

	// Look for the first sync token in the first 187 bytes
	for (var i = 0; i < 187; i++) {
		if (this.bits.bytes[byteIndex + i] === 0x47) {

			// Look for 4 more sync tokens, each 188 bytes appart
			var foundSync = true;
			for (var j = 1; j < 5; j++) {
				if (this.bits.bytes[byteIndex + i + 188 * j] !== 0x47) {
					foundSync = false;
					break;
				}
			}

			if (foundSync) {
				this.bits.index = (byteIndex + i + 1) << 3;
				return true;
			}
		}
	}

	// In theory, we shouldn't arrive here. If we do, we had enough data but
	// still didn't find sync - this can only happen if we were fed garbage
	// data. Check your source!
	console.warn('JSMpeg: Possible garbage data. Skipping.');
	this.bits.skip(187 << 3);
	return false;
};

TS.prototype.packetStart = function(pi, pts, payloadLength) {
	pi.totalLength = payloadLength;
	pi.currentLength = 0;
	pi.pts = pts;
};

TS.prototype.packetAddData = function(pi, start, end) {
	pi.buffers.push(this.bits.bytes.subarray(start, end));
	pi.currentLength += end - start;

	var complete = (pi.totalLength !== 0 && pi.currentLength >= pi.totalLength);
	return complete;
};

TS.prototype.packetComplete = function(pi) {
	pi.destination.write(pi.pts, pi.buffers);
	pi.totalLength = 0;
	pi.currentLength = 0;
	pi.buffers = [];
};

TS.STREAM = {
	PACK_HEADER: 0xBA,
	SYSTEM_HEADER: 0xBB,
	PROGRAM_MAP: 0xBC,
	PRIVATE_1: 0xBD,
	PADDING: 0xBE,
	PRIVATE_2: 0xBF,
	AUDIO_1: 0xC0,
	VIDEO_1: 0xE0,
	DIRECTORY: 0xFF
};

return TS;

})();