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niandeng
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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package org.mangui.hls.demux {
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import flash.utils.ByteArray;
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import org.mangui.hls.model.AudioTrack;
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import org.mangui.hls.flv.FLVTag;
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CONFIG::LOGGING {
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import org.mangui.hls.utils.Log;
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}
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public class MP3Demuxer implements Demuxer {
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/* MPEG1-Layer3 syncword */
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private static const SYNCWORD : uint = 0xFFFB;
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private static const RATES : Array = [44100, 48000, 32000];
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private static const BIT_RATES : Array = [0, 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 160000, 192000, 224000, 256000, 320000, 0];
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private static const SAMPLES_PER_FRAME : uint = 1152;
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/** Byte data to be read **/
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private var _data : ByteArray;
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/* callback functions for audio selection, and parsing progress/complete */
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private var _callback_audioselect : Function;
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private var _callback_progress : Function;
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private var _callback_complete : Function;
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private var _callback_error : Function;
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private var _callback_id3tag : Function;
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/** append new data */
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public function append(data : ByteArray) : void {
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if (_data == null) {
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_data = new ByteArray();
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}
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_data.writeBytes(data);
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}
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/** cancel demux operation */
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public function cancel() : void {
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_data = null;
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}
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public function get audioExpected() : Boolean {
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return true;
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}
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public function get videoExpected() : Boolean {
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return false;
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}
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public function notifycomplete() : void {
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CONFIG::LOGGING {
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Log.debug("MP3: extracting MP3 tags");
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}
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var audioTags : Vector.<FLVTag> = new Vector.<FLVTag>();
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/* parse MP3, convert Elementary Streams to TAG */
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_data.position = 0;
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var id3 : ID3 = new ID3(_data);
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// MP3 should contain ID3 tag filled with a timestamp
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var frames : Vector.<AudioFrame> = getFrames(_data, _data.position);
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var audioTag : FLVTag;
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var stamp : int;
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var i : int = 0;
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while (i < frames.length) {
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stamp = Math.round(id3.timestamp + i * 1024 * 1000 / frames[i].rate);
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audioTag = new FLVTag(FLVTag.MP3_RAW, stamp, stamp, false);
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if (i != frames.length - 1) {
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audioTag.push(_data, frames[i].start, frames[i].length);
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} else {
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audioTag.push(_data, frames[i].start, _data.length - frames[i].start);
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}
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audioTag.build();
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audioTags.push(audioTag);
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i++;
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}
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var audiotracks : Vector.<AudioTrack> = new Vector.<AudioTrack>();
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audiotracks.push(new AudioTrack('MP3 ES', AudioTrack.FROM_DEMUX, 0, true,false));
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// report unique audio track. dont check return value as obviously the track will be selected
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_callback_audioselect(audiotracks);
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CONFIG::LOGGING {
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Log.debug("MP3: all tags extracted, callback demux");
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}
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_data = null;
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if(id3.tags.length) {
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_callback_id3tag(id3.tags);
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}
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_callback_progress(audioTags);
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_callback_complete();
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}
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public function MP3Demuxer(callback_audioselect : Function,
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callback_progress : Function,
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callback_complete : Function,
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callback_error : Function,
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callback_id3tag : Function) : void {
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_callback_audioselect = callback_audioselect;
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_callback_progress = callback_progress;
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_callback_complete = callback_complete;
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_callback_error = callback_error;
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_callback_id3tag = callback_id3tag;
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};
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public static function probe(data : ByteArray) : Boolean {
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var pos : uint = data.position;
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var id3 : ID3 = new ID3(data);
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// MP3 should contain ID3 tag filled with a timestamp
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if (id3.hasTimestamp) {
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var afterID3 : uint = data.position;
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while (data.bytesAvailable > 1 && (data.position - afterID3) < 100) {
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// Check for MP3 header
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var short : uint = data.readUnsignedShort();
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if (short == SYNCWORD) {
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CONFIG::LOGGING {
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Log.debug2("MP3: found header " + short + "@ " + (data.position-2));
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}
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data.position = pos;
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return true;
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} else {
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data.position--;
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}
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}
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data.position = pos;
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}
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return false;
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}
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private static function getFrames(data : ByteArray, position : uint) : Vector.<AudioFrame> {
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var frames : Vector.<AudioFrame> = new Vector.<AudioFrame>();
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var frame_start : uint;
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var frame_length : uint;
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var id3 : ID3 = new ID3(data);
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position += id3.len;
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// Get raw MP3 frames from audio stream.
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data.position = position;
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// we need at least 3 bytes, 2 for sync word, 1 for flags
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while (data.bytesAvailable > 3) {
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frame_start = data.position;
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// frame header described here : http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html
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var short : uint = data.readUnsignedShort();
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if (short == SYNCWORD) {
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var flag : uint = data.readByte();
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// (15,12)=(&0xf0 >>4) Bitrate index
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var bitrate : uint = BIT_RATES[(flag & 0xf0) >> 4];
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// (11,10)=(&0xc >> 2) Sampling rate frequency index (values are in Hz)
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var samplerate : uint = RATES[(flag & 0xc) >> 2];
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// (9)=(&2 >>1) Padding bit
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var padbit : uint = (flag & 2) >> 1;
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frame_length = (SAMPLES_PER_FRAME / 8) * bitrate / samplerate + padbit;
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frame_length = Math.round(frame_length);
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data.position = data.position + (frame_length - 3);
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frames.push(new AudioFrame(frame_start, frame_length, frame_length, samplerate));
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} else {
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data.position = data.position - 1;
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}
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}
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data.position = position;
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return frames;
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}
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}
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}
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