var recLength = 0,
recBuffersL = [], recBuffersR = [], sampleRate;
this.onmessage = function(e){
switch(e.data.command){ case 'init': init(e.data.config); break; case 'record': record(e.data.buffer); break; case 'exportWAV': exportWAV(e.data.type); break; case 'getBuffer': getBuffer(); break; case 'clear': clear(); break; }
};
function init(config){
sampleRate = config.sampleRate;
}
function record(inputBuffer){
recBuffersL.push(inputBuffer[0]); recBuffersR.push(inputBuffer[1]); recLength += inputBuffer[0].length;
}
function exportWAV(type){
var bufferL = mergeBuffers(recBuffersL, recLength); var bufferR = mergeBuffers(recBuffersR, recLength); var interleaved = interleave(bufferL, bufferR); var dataview = encodeWAV(interleaved); var audioBlob = new Blob([dataview], { type: type }); this.postMessage(audioBlob);
}
function getBuffer() {
var buffers = []; buffers.push( mergeBuffers(recBuffersL, recLength) ); buffers.push( mergeBuffers(recBuffersR, recLength) ); this.postMessage(buffers);
}
function clear(){
recLength = 0; recBuffersL = []; recBuffersR = [];
}
function mergeBuffers(recBuffers, recLength){
var result = new Float32Array(recLength); var offset = 0; for (var i = 0; i < recBuffers.length; i++){ result.set(recBuffers[i], offset); offset += recBuffers[i].length; } return result;
}
function interleave(inputL, inputR){
var length = inputL.length + inputR.length; var result = new Float32Array(length); var index = 0, inputIndex = 0; while (index < length){ result[index++] = inputL[inputIndex]; result[index++] = inputR[inputIndex]; inputIndex++; } return result;
}
function floatTo16BitPCM(output, offset, input){
for (var i = 0; i < input.length; i++, offset+=2){ var s = Math.max(-1, Math.min(1, input[i])); output.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true); }
}
function writeString(view, offset, string){
for (var i = 0; i < string.length; i++){ view.setUint8(offset + i, string.charCodeAt(i)); }
}
function encodeWAV(samples){
var buffer = new ArrayBuffer(44 + samples.length * 2); var view = new DataView(buffer); /* RIFF identifier */ writeString(view, 0, 'RIFF'); /* RIFF chunk length */ view.setUint32(4, 36 + samples.length * 2, true); /* RIFF type */ writeString(view, 8, 'WAVE'); /* format chunk identifier */ writeString(view, 12, 'fmt '); /* format chunk length */ view.setUint32(16, 16, true); /* sample format (raw) */ view.setUint16(20, 1, true); /* channel count */ view.setUint16(22, 2, true); /* sample rate */ view.setUint32(24, sampleRate, true); /* byte rate (sample rate * block align) */ view.setUint32(28, sampleRate * 4, true); /* block align (channel count * bytes per sample) */ view.setUint16(32, 4, true); /* bits per sample */ view.setUint16(34, 16, true); /* data chunk identifier */ writeString(view, 36, 'data'); /* data chunk length */ view.setUint32(40, samples.length * 2, true); floatTo16BitPCM(view, 44, samples); return view;
}