Decrease bitrate on WAV file created with recorderjs

Question

I\'m trying to use recorderjs on an app engine site where users upload short audio recordings (say, 1 to a dozen seconds long). I\'ve noticed that the WAV files I\'m uploadi

Answer 1

In my case Chrome records audio at 96kHz and Firefox at 44.1kHz, that makes huge WAV files. I implemented a downsampling function inside recorderWorker.js where you can select the sample ratio you want, like 16000.

function downsampleBuffer(buffer, rate) {
    if (rate == sampleRate) {
        return buffer;
    }
    if (rate > sampleRate) {
        throw "downsampling rate show be smaller than original sample rate";
    }
    var sampleRateRatio = sampleRate / rate;
    var newLength = Math.round(buffer.length / sampleRateRatio);
    var result = new Float32Array(newLength);
    var offsetResult = 0;
    var offsetBuffer = 0;
    while (offsetResult < result.length) {
        var nextOffsetBuffer = Math.round((offsetResult + 1) * sampleRateRatio);
        var accum = 0, count = 0;
        for (var i = offsetBuffer; i < nextOffsetBuffer && i < buffer.length; i++) {
            accum += buffer[i];
            count++;
        }
        result[offsetResult] = accum / count;
        offsetResult++;
        offsetBuffer = nextOffsetBuffer;
    }
    return result;
}

and i call it when exporting the wav file:

function exportWAV(rate, type) {
    var bufferL = mergeBuffers(recBuffersL, recLength);
    var bufferR = mergeBuffers(recBuffersR, recLength);
    var interleaved = interleave(bufferL, bufferR);
    var downsampledBuffer = downsampleBuffer(interleaved, rate);
    var dataview = encodeWAV(rate, downsampledBuffer, false);
    var audioBlob = new Blob([ dataview ], {
        type : type
    });

    this.postMessage(audioBlob);
}