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implement adpcdm synchronization, refs #203

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This commit is contained in:
Jakob Ketterl 2021-07-06 19:40:06 +02:00
parent 1a9bcdeb07
commit 14eb71c8de
1 changed files with 42 additions and 1 deletions
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43
htdocs/lib/AudioEngine.js
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@ -282,7 +282,7 @@ AudioEngine.prototype.processAudio = function(data, resampler) {
var buffer;
if (this.compression === "adpcm") {
//resampling & ADPCM
buffer = this.audioCodec.decode(new Uint8Array(data));
buffer = this.audioCodec.decodeWithSync(new Uint8Array(data));
} else {
buffer = new Int16Array(data);
}
@ -328,6 +328,10 @@ ImaAdpcmCodec.prototype.reset = function() {
this.stepIndex = 0;
this.predictor = 0;
this.step = 0;
this.synchronized = 0;
this.syncWord = "SYNC";
this.syncCounter = 0;
this.skip = 0;
};
ImaAdpcmCodec.imaIndexTable = [ -1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8 ];
@ -353,6 +357,43 @@ ImaAdpcmCodec.prototype.decode = function(data) {
return output;
};
ImaAdpcmCodec.prototype.decodeWithSync = function(data) {
var output = new Int16Array(data.length * 2);
var index = this.skip;
var oi = 0;
while (index < data.length) {
while (this.synchronized < 4 && index < data.length) {
if (data[index] === this.syncWord.charCodeAt(this.synchronized)) {
this.synchronized++;
} else {
this.synchronized = 0;
}
index++;
if (this.synchronized === 4) {
if (index + 4 < data.length) {
var syncData = new Int16Array(data.buffer.slice(index, index + 4));
this.stepIndex = syncData[0];
this.predictor = syncData[1];
}
this.syncCounter = 1000;
index += 4;
break;
}
}
while (index < data.length) {
if (this.syncCounter-- < 0) {
this.synchronized = 0;
break;
}
output[oi++] = this.decodeNibble(data[index] & 0x0F);
output[oi++] = this.decodeNibble(data[index] >> 4);
index++;
}
}
this.skip = index - data.length;
return output.slice(0, oi);
};
ImaAdpcmCodec.prototype.decodeNibble = function(nibble) {
this.stepIndex += ImaAdpcmCodec.imaIndexTable[nibble];
this.stepIndex = Math.min(Math.max(this.stepIndex, 0), 88);