The web audio API down is 44.1kHz in Javascript
I am using RecorderJS to record a microphone stream from a user. The default export is a 44.1 kHz, 16 bit WAV file. Is there anyway I can reduce this to 11 kHz or 16 kHz if it's not weird? Is there anyway I can get a 16bit 16x WAV file from the getUserMedia Web Audio API stream using only javascript?
I am trying to reduce the file size thus saving a lot of bandwidth for the users. Thank.
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Edit: one more thing, you can also only send one feed instead of ...
I'm not sure if this is the right way, but I did by doing interpolation of the data received from the microphone.I assume you are grabbing your data from the microphone something like this,
this.node.onaudioprocess = function(e){
if (!recording) return;
worker.postMessage({
command: 'record',
buffer: [
e.inputBuffer.getChannelData(0),
e.inputBuffer.getChannelData(1)
]
});
}
now change it to
var oldSampleRate = 44100, newSampleRate = 16000;
this.node.onaudioprocess = function(e){
var leftData = e.inputBuffer.getChannelData(0);
var rightData = e.inputBuffer.getChannelData(1);
leftData = interpolateArray(leftData, leftData.length * (newSampleRate/oldSampleRate) );
rightData = interpolateArray(rightData, rightData.length * (newSampleRate/oldSampleRate) );
if (!recording) return;
worker.postMessage({
command: 'record',
buffer: [
leftData,
rightData
]
});
}
function interpolateArray(data, fitCount) {
var linearInterpolate = function (before, after, atPoint) {
return before + (after - before) * atPoint;
};
var newData = new Array();
var springFactor = new Number((data.length - 1) / (fitCount - 1));
newData[0] = data[0]; // for new allocation
for ( var i = 1; i < fitCount - 1; i++) {
var tmp = i * springFactor;
var before = new Number(Math.floor(tmp)).toFixed();
var after = new Number(Math.ceil(tmp)).toFixed();
var atPoint = tmp - before;
newData[i] = linearInterpolate(data[before], data[after], atPoint);
}
newData[fitCount - 1] = data[data.length - 1]; // for new allocation
return newData;
};
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