index.js
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/**
* mux.js
*
* Copyright (c) 2016 Brightcove
* All rights reserved.
*
* A stream-based aac to mp4 converter. This utility can be used to
* deliver mp4s to a SourceBuffer on platforms that support native
* Media Source Extensions.
*/
'use strict';
var Stream = require('../utils/stream.js');
// Constants
var AacStream;
/**
* Splits an incoming stream of binary data into ADTS and ID3 Frames.
*/
AacStream = function() {
var
everything = new Uint8Array(),
timeStamp = 0;
AacStream.prototype.init.call(this);
this.setTimestamp = function(timestamp) {
timeStamp = timestamp;
};
this.parseId3TagSize = function(header, byteIndex) {
var
returnSize = (header[byteIndex + 6] << 21) |
(header[byteIndex + 7] << 14) |
(header[byteIndex + 8] << 7) |
(header[byteIndex + 9]),
flags = header[byteIndex + 5],
footerPresent = (flags & 16) >> 4;
if (footerPresent) {
return returnSize + 20;
}
return returnSize + 10;
};
this.parseAdtsSize = function(header, byteIndex) {
var
lowThree = (header[byteIndex + 5] & 0xE0) >> 5,
middle = header[byteIndex + 4] << 3,
highTwo = header[byteIndex + 3] & 0x3 << 11;
return (highTwo | middle) | lowThree;
};
this.push = function(bytes) {
var
frameSize = 0,
byteIndex = 0,
bytesLeft,
chunk,
packet,
tempLength;
// If there are bytes remaining from the last segment, prepend them to the
// bytes that were pushed in
if (everything.length) {
tempLength = everything.length;
everything = new Uint8Array(bytes.byteLength + tempLength);
everything.set(everything.subarray(0, tempLength));
everything.set(bytes, tempLength);
} else {
everything = bytes;
}
while (everything.length - byteIndex >= 3) {
if ((everything[byteIndex] === 'I'.charCodeAt(0)) &&
(everything[byteIndex + 1] === 'D'.charCodeAt(0)) &&
(everything[byteIndex + 2] === '3'.charCodeAt(0))) {
// Exit early because we don't have enough to parse
// the ID3 tag header
if (everything.length - byteIndex < 10) {
break;
}
// check framesize
frameSize = this.parseId3TagSize(everything, byteIndex);
// Exit early if we don't have enough in the buffer
// to emit a full packet
if (frameSize > everything.length) {
break;
}
chunk = {
type: 'timed-metadata',
data: everything.subarray(byteIndex, byteIndex + frameSize)
};
this.trigger('data', chunk);
byteIndex += frameSize;
continue;
} else if ((everything[byteIndex] & 0xff === 0xff) &&
((everything[byteIndex + 1] & 0xf0) === 0xf0)) {
// Exit early because we don't have enough to parse
// the ADTS frame header
if (everything.length - byteIndex < 7) {
break;
}
frameSize = this.parseAdtsSize(everything, byteIndex);
// Exit early if we don't have enough in the buffer
// to emit a full packet
if (frameSize > everything.length) {
break;
}
packet = {
type: 'audio',
data: everything.subarray(byteIndex, byteIndex + frameSize),
pts: timeStamp,
dts: timeStamp
};
this.trigger('data', packet);
byteIndex += frameSize;
continue;
}
byteIndex++;
}
bytesLeft = everything.length - byteIndex;
if (bytesLeft > 0) {
everything = everything.subarray(byteIndex);
} else {
everything = new Uint8Array();
}
};
};
AacStream.prototype = new Stream();
module.exports = AacStream;