154 lines
3.8 KiB
JavaScript
154 lines
3.8 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 ExpGolomb;
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/**
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* Parser for exponential Golomb codes, a variable-bitwidth number encoding
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* scheme used by h264.
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*/
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ExpGolomb = function ExpGolomb(workingData) {
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var // the number of bytes left to examine in workingData
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workingBytesAvailable = workingData.byteLength,
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// the current word being examined
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workingWord = 0,
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// :uint
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// the number of bits left to examine in the current word
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workingBitsAvailable = 0; // :uint;
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// ():uint
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this.length = function () {
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return 8 * workingBytesAvailable;
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}; // ():uint
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this.bitsAvailable = function () {
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return 8 * workingBytesAvailable + workingBitsAvailable;
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}; // ():void
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this.loadWord = function () {
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var position = workingData.byteLength - workingBytesAvailable,
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workingBytes = new Uint8Array(4),
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availableBytes = Math.min(4, workingBytesAvailable);
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if (availableBytes === 0) {
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throw new Error('no bytes available');
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}
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workingBytes.set(workingData.subarray(position, position + availableBytes));
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workingWord = new DataView(workingBytes.buffer).getUint32(0); // track the amount of workingData that has been processed
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workingBitsAvailable = availableBytes * 8;
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workingBytesAvailable -= availableBytes;
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}; // (count:int):void
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this.skipBits = function (count) {
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var skipBytes; // :int
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if (workingBitsAvailable > count) {
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workingWord <<= count;
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workingBitsAvailable -= count;
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} else {
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count -= workingBitsAvailable;
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skipBytes = Math.floor(count / 8);
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count -= skipBytes * 8;
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workingBytesAvailable -= skipBytes;
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this.loadWord();
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workingWord <<= count;
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workingBitsAvailable -= count;
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}
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}; // (size:int):uint
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this.readBits = function (size) {
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var bits = Math.min(workingBitsAvailable, size),
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// :uint
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valu = workingWord >>> 32 - bits; // :uint
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// if size > 31, handle error
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workingBitsAvailable -= bits;
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if (workingBitsAvailable > 0) {
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workingWord <<= bits;
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} else if (workingBytesAvailable > 0) {
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this.loadWord();
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}
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bits = size - bits;
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if (bits > 0) {
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return valu << bits | this.readBits(bits);
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}
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return valu;
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}; // ():uint
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this.skipLeadingZeros = function () {
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var leadingZeroCount; // :uint
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for (leadingZeroCount = 0; leadingZeroCount < workingBitsAvailable; ++leadingZeroCount) {
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if ((workingWord & 0x80000000 >>> leadingZeroCount) !== 0) {
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// the first bit of working word is 1
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workingWord <<= leadingZeroCount;
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workingBitsAvailable -= leadingZeroCount;
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return leadingZeroCount;
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}
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} // we exhausted workingWord and still have not found a 1
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this.loadWord();
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return leadingZeroCount + this.skipLeadingZeros();
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}; // ():void
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this.skipUnsignedExpGolomb = function () {
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this.skipBits(1 + this.skipLeadingZeros());
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}; // ():void
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this.skipExpGolomb = function () {
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this.skipBits(1 + this.skipLeadingZeros());
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}; // ():uint
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this.readUnsignedExpGolomb = function () {
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var clz = this.skipLeadingZeros(); // :uint
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return this.readBits(clz + 1) - 1;
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}; // ():int
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this.readExpGolomb = function () {
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var valu = this.readUnsignedExpGolomb(); // :int
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if (0x01 & valu) {
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// the number is odd if the low order bit is set
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return 1 + valu >>> 1; // add 1 to make it even, and divide by 2
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}
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return -1 * (valu >>> 1); // divide by two then make it negative
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}; // Some convenience functions
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// :Boolean
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this.readBoolean = function () {
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return this.readBits(1) === 1;
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}; // ():int
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this.readUnsignedByte = function () {
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return this.readBits(8);
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};
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this.loadWord();
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};
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module.exports = ExpGolomb; |