implement adpcdm synchronization, refs #203
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@ -282,7 +282,7 @@ AudioEngine.prototype.processAudio = function(data, resampler) {
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var buffer;
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if (this.compression === "adpcm") {
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//resampling & ADPCM
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buffer = this.audioCodec.decode(new Uint8Array(data));
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buffer = this.audioCodec.decodeWithSync(new Uint8Array(data));
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} else {
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buffer = new Int16Array(data);
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}
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@ -328,6 +328,10 @@ ImaAdpcmCodec.prototype.reset = function() {
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this.stepIndex = 0;
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this.predictor = 0;
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this.step = 0;
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this.synchronized = 0;
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this.syncWord = "SYNC";
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this.syncCounter = 0;
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this.skip = 0;
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};
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ImaAdpcmCodec.imaIndexTable = [ -1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8 ];
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@ -353,6 +357,43 @@ ImaAdpcmCodec.prototype.decode = function(data) {
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return output;
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};
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ImaAdpcmCodec.prototype.decodeWithSync = function(data) {
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var output = new Int16Array(data.length * 2);
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var index = this.skip;
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var oi = 0;
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while (index < data.length) {
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while (this.synchronized < 4 && index < data.length) {
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if (data[index] === this.syncWord.charCodeAt(this.synchronized)) {
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this.synchronized++;
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} else {
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this.synchronized = 0;
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}
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index++;
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if (this.synchronized === 4) {
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if (index + 4 < data.length) {
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var syncData = new Int16Array(data.buffer.slice(index, index + 4));
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this.stepIndex = syncData[0];
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this.predictor = syncData[1];
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}
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this.syncCounter = 1000;
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index += 4;
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break;
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}
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}
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while (index < data.length) {
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if (this.syncCounter-- < 0) {
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this.synchronized = 0;
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break;
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}
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output[oi++] = this.decodeNibble(data[index] & 0x0F);
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output[oi++] = this.decodeNibble(data[index] >> 4);
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index++;
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}
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}
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this.skip = index - data.length;
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return output.slice(0, oi);
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};
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ImaAdpcmCodec.prototype.decodeNibble = function(nibble) {
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this.stepIndex += ImaAdpcmCodec.imaIndexTable[nibble];
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this.stepIndex = Math.min(Math.max(this.stepIndex, 0), 88);
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