128 lines
No EOL
4 KiB
JavaScript
128 lines
No EOL
4 KiB
JavaScript
/**
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* mux.js
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*
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* Copyright (c) Brightcove
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* Licensed Apache-2.0 https://github.com/videojs/mux.js/blob/master/LICENSE
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*/
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'use strict';
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var Stream = require('../utils/stream.js');
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var ONE_SECOND_IN_TS = require('../utils/clock').ONE_SECOND_IN_TS;
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var _AdtsStream;
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var ADTS_SAMPLING_FREQUENCIES = [96000, 88200, 64000, 48000, 44100, 32000, 24000, 22050, 16000, 12000, 11025, 8000, 7350];
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/*
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* Accepts a ElementaryStream and emits data events with parsed
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* AAC Audio Frames of the individual packets. Input audio in ADTS
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* format is unpacked and re-emitted as AAC frames.
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*
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* @see http://wiki.multimedia.cx/index.php?title=ADTS
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* @see http://wiki.multimedia.cx/?title=Understanding_AAC
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*/
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_AdtsStream = function AdtsStream(handlePartialSegments) {
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var buffer,
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frameNum = 0;
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_AdtsStream.prototype.init.call(this);
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this.push = function (packet) {
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var i = 0,
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frameLength,
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protectionSkipBytes,
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frameEnd,
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oldBuffer,
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sampleCount,
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adtsFrameDuration;
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if (!handlePartialSegments) {
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frameNum = 0;
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}
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if (packet.type !== 'audio') {
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// ignore non-audio data
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return;
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} // Prepend any data in the buffer to the input data so that we can parse
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// aac frames the cross a PES packet boundary
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if (buffer) {
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oldBuffer = buffer;
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buffer = new Uint8Array(oldBuffer.byteLength + packet.data.byteLength);
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buffer.set(oldBuffer);
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buffer.set(packet.data, oldBuffer.byteLength);
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} else {
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buffer = packet.data;
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} // unpack any ADTS frames which have been fully received
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// for details on the ADTS header, see http://wiki.multimedia.cx/index.php?title=ADTS
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while (i + 5 < buffer.length) {
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// Look for the start of an ADTS header..
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if (buffer[i] !== 0xFF || (buffer[i + 1] & 0xF6) !== 0xF0) {
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// If a valid header was not found, jump one forward and attempt to
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// find a valid ADTS header starting at the next byte
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i++;
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continue;
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} // The protection skip bit tells us if we have 2 bytes of CRC data at the
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// end of the ADTS header
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protectionSkipBytes = (~buffer[i + 1] & 0x01) * 2; // Frame length is a 13 bit integer starting 16 bits from the
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// end of the sync sequence
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frameLength = (buffer[i + 3] & 0x03) << 11 | buffer[i + 4] << 3 | (buffer[i + 5] & 0xe0) >> 5;
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sampleCount = ((buffer[i + 6] & 0x03) + 1) * 1024;
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adtsFrameDuration = sampleCount * ONE_SECOND_IN_TS / ADTS_SAMPLING_FREQUENCIES[(buffer[i + 2] & 0x3c) >>> 2];
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frameEnd = i + frameLength; // If we don't have enough data to actually finish this ADTS frame, return
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// and wait for more data
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if (buffer.byteLength < frameEnd) {
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return;
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} // Otherwise, deliver the complete AAC frame
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this.trigger('data', {
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pts: packet.pts + frameNum * adtsFrameDuration,
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dts: packet.dts + frameNum * adtsFrameDuration,
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sampleCount: sampleCount,
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audioobjecttype: (buffer[i + 2] >>> 6 & 0x03) + 1,
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channelcount: (buffer[i + 2] & 1) << 2 | (buffer[i + 3] & 0xc0) >>> 6,
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samplerate: ADTS_SAMPLING_FREQUENCIES[(buffer[i + 2] & 0x3c) >>> 2],
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samplingfrequencyindex: (buffer[i + 2] & 0x3c) >>> 2,
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// assume ISO/IEC 14496-12 AudioSampleEntry default of 16
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samplesize: 16,
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data: buffer.subarray(i + 7 + protectionSkipBytes, frameEnd)
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});
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frameNum++; // If the buffer is empty, clear it and return
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if (buffer.byteLength === frameEnd) {
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buffer = undefined;
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return;
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} // Remove the finished frame from the buffer and start the process again
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buffer = buffer.subarray(frameEnd);
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}
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};
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this.flush = function () {
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frameNum = 0;
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this.trigger('done');
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};
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this.reset = function () {
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buffer = void 0;
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this.trigger('reset');
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};
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this.endTimeline = function () {
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buffer = void 0;
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this.trigger('endedtimeline');
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};
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};
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_AdtsStream.prototype = new Stream();
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module.exports = _AdtsStream; |