How to convert AudioBuffer to wav file?

Question

I'm trying to convert an AudioBuffer into a wav file that I can download. I tried 2 methods: The first one, I record all the sounds going threw a mediaRecorder and do this:

App.model.mediaRecorder.ondataavailable = function(evt) {
   // push each chunk (blobs) in an array
    //console.log(evt.data)
   App.model.chunks.push(evt.data);
 };

 App.model.mediaRecorder.onstop = function(evt) {
   // Make blob out of our blobs, and open it.
   var blob = new Blob(App.model.chunks, { 'type' : 'audio/wav; codecs=opus' });
   createDownloadLink(blob);

 };

I create a chunk table containing blobs and then create a new Blob with these chunks. Then in the function "createDownloadLink()" I create an audio node and a download link:

function createDownloadLink(blob) {

  var url = URL.createObjectURL(blob);
  var li = document.createElement('li');
  var au = document.createElement('audio');
  li.className = "recordedElement";
  var hf = document.createElement('a');
  li.style.textDecoration ="none";
  au.controls = true;
  au.src = url;
  hf.href = url;
  hf.download = 'myrecording' + App.model.countRecordings + ".wav";
  hf.innerHTML = hf.download;
  li.appendChild(au);
  li.appendChild(hf);
  recordingslist.appendChild(li);

}

The audio node is created and I can listen to the sound that I recorded so everything seems to work. But when I download the file it can't be read by any player. I think it's because it's not encoded in WAV so it's not understand.

The second method is the same than above except for the "createDownloadLink()" function.

function createDownloadLink(blob) {


  var reader = new FileReader();
  reader.readAsArrayBuffer(blob);
  App.model.sourceBuffer = App.model.audioCtx.createBufferSource();

  reader.onloadend = function()
  {
      App.model.recordBuffer = reader.result;
      App.model.audioCtx.decodeAudioData(App.model.recordBuffer, function(decodedData)
                                        {
          App.model.sourceBuffer.buffer = decodedData;

      })
  }

Here I get an AudioBuffer of the sounds I recorded, but I didn't find how to convert it into a WAV file...

Answer 1

Can you use a variation of this? https://gist.github.com/asanoboy/3979747

Maybe something like this?

var wav = createWavFromBuffer(convertBlock(decodedData), 44100); 
// Then call wav.getBuffer or wav.getWavInt16Array() for the WAV-RIFF formatted data

The other functions here:

class Wav {
    constructor(opt_params) {
        this._sampleRate = opt_params && opt_params.sampleRate ? opt_params.sampleRate : 44100;
        this._channels = opt_params && opt_params.channels ? opt_params.channels : 2;
        this._eof = true;
        this._bufferNeedle = 0;
        this._buffer;
    }
    setBuffer(buffer) {
        this._buffer = this.getWavInt16Array(buffer);
        this._bufferNeedle = 0;
        this._internalBuffer = '';
        this._hasOutputHeader = false;
        this._eof = false;
    }
    getBuffer(len) {
        var rt;
        if( this._bufferNeedle + len >= this._buffer.length ){
            rt = new Int16Array(this._buffer.length - this._bufferNeedle);
            this._eof = true;
        }
        else {
            rt = new Int16Array(len);
        }
        for(var i=0; i<rt.length; i++){
            rt[i] = this._buffer[i+this._bufferNeedle];
        }
        this._bufferNeedle += rt.length;
        return  rt.buffer;
    }
    eof() {
        return this._eof;
    }
    getWavInt16Array(buffer) {

        var intBuffer = new Int16Array(buffer.length + 23), tmp;

        intBuffer[0] = 0x4952; // "RI"
        intBuffer[1] = 0x4646; // "FF"

        intBuffer[2] = (2*buffer.length + 15) & 0x0000ffff; // RIFF size
        intBuffer[3] = ((2*buffer.length + 15) & 0xffff0000) >> 16; // RIFF size

        intBuffer[4] = 0x4157; // "WA"
        intBuffer[5] = 0x4556; // "VE"

        intBuffer[6] = 0x6d66; // "fm"
        intBuffer[7] = 0x2074; // "t "

        intBuffer[8] = 0x0012; // fmt chunksize: 18
        intBuffer[9] = 0x0000; //

        intBuffer[10] = 0x0001; // format tag : 1 
        intBuffer[11] = this._channels; // channels: 2

        intBuffer[12] = this._sampleRate & 0x0000ffff; // sample per sec
        intBuffer[13] = (this._sampleRate & 0xffff0000) >> 16; // sample per sec

        intBuffer[14] = (2*this._channels*this._sampleRate) & 0x0000ffff; // byte per sec
        intBuffer[15] = ((2*this._channels*this._sampleRate) & 0xffff0000) >> 16; // byte per sec

        intBuffer[16] = 0x0004; // block align
        intBuffer[17] = 0x0010; // bit per sample
        intBuffer[18] = 0x0000; // cb size
        intBuffer[19] = 0x6164; // "da"
        intBuffer[20] = 0x6174; // "ta"
        intBuffer[21] = (2*buffer.length) & 0x0000ffff; // data size[byte]
        intBuffer[22] = ((2*buffer.length) & 0xffff0000) >> 16; // data size[byte]  

        for (var i = 0; i < buffer.length; i++) {
            tmp = buffer[i];
            if (tmp >= 1) {
                intBuffer[i+23] = (1 << 15) - 1;
            }
            else if (tmp <= -1) {
                intBuffer[i+23] = -(1 << 15);
            }
            else {
                intBuffer[i+23] = Math.round(tmp * (1 << 15));
            }
        }

        return intBuffer;
    }
}

// factory
function createWavFromBuffer(buffer, sampleRate) {
  var wav = new Wav({
      sampleRate: sampleRate,
      channels: 1
  });
  wav.setBuffer(buffer);
  return wav;
}


// ArrayBuffer -> Float32Array
var convertBlock = function(buffer) {
    var incomingData = new Uint8Array(buffer);
    var i, l = incomingData.length;
    var outputData = new Float32Array(incomingData.length);
    for (i = 0; i < l; i++) {
        outputData[i] = (incomingData[i] - 128) / 128.0;
    }
    return outputData;
}