shaka-player
Version:
DASH/EME video player library
197 lines (178 loc) • 5.53 kB
JavaScript
/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.provide('shaka.transmuxer.MpegAudio');
/**
* MPEG parser utils
*
* @see https://en.wikipedia.org/wiki/MP3
*/
shaka.transmuxer.MpegAudio = class {
/**
* @param {!Uint8Array} data
* @param {!number} offset
* @return {?{sampleRate: number, channelCount: number,
* frameLength: number, samplesPerFrame: number}}
*/
static parseHeader(data, offset) {
const MpegAudio = shaka.transmuxer.MpegAudio;
const mpegVersion = (data[offset + 1] >> 3) & 3;
const mpegLayer = (data[offset + 1] >> 1) & 3;
const bitRateIndex = (data[offset + 2] >> 4) & 15;
const sampleRateIndex = (data[offset + 2] >> 2) & 3;
if (mpegVersion !== 1 && bitRateIndex !== 0 &&
bitRateIndex !== 15 && sampleRateIndex !== 3) {
const paddingBit = (data[offset + 2] >> 1) & 1;
const channelMode = data[offset + 3] >> 6;
let columnInBitrates = 0;
if (mpegVersion === 3) {
columnInBitrates = 3 - mpegLayer;
} else {
columnInBitrates = mpegLayer === 3 ? 3 : 4;
}
const bitRate = MpegAudio.BITRATES_MAP_[
columnInBitrates * 14 + bitRateIndex - 1] * 1000;
const columnInSampleRates =
mpegVersion === 3 ? 0 : mpegVersion === 2 ? 1 : 2;
const sampleRate = MpegAudio.SAMPLING_RATE_MAP_[
columnInSampleRates * 3 + sampleRateIndex];
// If bits of channel mode are `11` then it is a single channel (Mono)
const channelCount = channelMode === 3 ? 1 : 2;
const sampleCoefficient =
MpegAudio.SAMPLES_COEFFICIENTS_[mpegVersion][mpegLayer];
const bytesInSlot = MpegAudio.BYTES_IN_SLOT_[mpegLayer];
const samplesPerFrame = sampleCoefficient * 8 * bytesInSlot;
const frameLength =
Math.floor((sampleCoefficient * bitRate) / sampleRate + paddingBit) *
bytesInSlot;
const userAgent = navigator.userAgent || '';
// This affect to Tizen also for example.
const result = userAgent.match(/Chrome\/(\d+)/i);
const chromeVersion = result ? parseInt(result[1], 10) : 0;
const needChromeFix = !!chromeVersion && chromeVersion <= 87;
if (needChromeFix && mpegLayer === 2 &&
bitRate >= 224000 && channelMode === 0) {
// Work around bug in Chromium by setting channelMode
// to dual-channel (01) instead of stereo (00)
data[offset + 3] = data[offset + 3] | 0x80;
}
return {sampleRate, channelCount, frameLength, samplesPerFrame};
}
return null;
}
/**
* @param {!Uint8Array} data
* @param {!number} offset
* @return {boolean}
*/
static isHeaderPattern(data, offset) {
return (
data[offset] === 0xff &&
(data[offset + 1] & 0xe0) === 0xe0 &&
(data[offset + 1] & 0x06) !== 0x00
);
}
/**
* @param {!Uint8Array} data
* @param {!number} offset
* @return {boolean}
*/
static isHeader(data, offset) {
// Look for MPEG header | 1111 1111 | 111X XYZX | where X can be either
// 0 or 1 and Y or Z should be 1
// Layer bits (position 14 and 15) in header should be always different
// from 0 (Layer I or Layer II or Layer III)
// More info http://www.mp3-tech.org/programmer/frame_header.html
return offset + 1 < data.length &&
shaka.transmuxer.MpegAudio.isHeaderPattern(data, offset);
}
/**
* @param {!Uint8Array} data
* @param {!number} offset
* @return {boolean}
*/
static probe(data, offset) {
const MpegAudio = shaka.transmuxer.MpegAudio;
// same as isHeader but we also check that MPEG frame follows last
// MPEG frame or end of data is reached
if (offset + 1 < data.length &&
MpegAudio.isHeaderPattern(data, offset)) {
// MPEG header Length
const headerLength = 4;
// MPEG frame Length
const header = MpegAudio.parseHeader(data, offset);
let frameLength = headerLength;
if (header && header.frameLength) {
frameLength = header.frameLength;
}
const newOffset = offset + frameLength;
return newOffset === data.length ||
MpegAudio.isHeader(data, newOffset);
}
return false;
}
};
/**
* @private {!Array<number>}
*/
shaka.transmuxer.MpegAudio.BITRATES_MAP_ = [
32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 32, 48, 56,
64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 32, 40, 48, 56, 64, 80,
96, 112, 128, 160, 192, 224, 256, 320, 32, 48, 56, 64, 80, 96, 112, 128, 144,
160, 176, 192, 224, 256, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144,
160,
];
/**
* @private {!Array<number>}
*/
shaka.transmuxer.MpegAudio.SAMPLING_RATE_MAP_ = [
44100, 48000, 32000, 22050, 24000, 16000, 11025, 12000, 8000,
];
/**
* @private {!Array<!Array<number>>}
*/
shaka.transmuxer.MpegAudio.SAMPLES_COEFFICIENTS_ = [
// MPEG 2.5
[
0, // Reserved
72, // Layer3
144, // Layer2
12, // Layer1
],
// Reserved
[
0, // Reserved
0, // Layer3
0, // Layer2
0, // Layer1
],
// MPEG 2
[
0, // Reserved
72, // Layer3
144, // Layer2
12, // Layer1
],
// MPEG 1
[
0, // Reserved
144, // Layer3
144, // Layer2
12, // Layer1
],
];
/**
* @private {!Array<number>}
*/
shaka.transmuxer.MpegAudio.BYTES_IN_SLOT_ = [
0, // Reserved
1, // Layer3
1, // Layer2
4, // Layer1
];
/**
* @const {number}
*/
shaka.transmuxer.MpegAudio.MPEG_AUDIO_SAMPLE_PER_FRAME = 1152;