Blob to MP3

[nal-ws-001]

Can i change blob to mp3?

[Spodnet]

FileReader can do this, I do it to convert a blob mono wav to mp3

var audioBuffer;
var fileReader = new FileReader();
fileReader.onload = function(event) {
    audioBuffer = event.target.result;

    var wav = lamejs.WavHeader.readHeader(new DataView(audioBuffer));
    var samples = new Int16Array(audioBuffer, wav.dataOffset, wav.dataLen / 2);

    var channels = wav.channels;
    var sampleRate = wav.sampleRate;
    var kbps = 128;
    var mp3encoder = new lamejs.Mp3Encoder(channels, sampleRate, kbps);

    sampleBlockSize = 1152;

    var mp3Data = [];
    for (var i = 0; i < samples.length; i += sampleBlockSize) {
        sampleChunk = samples.subarray(i, i + sampleBlockSize);
        var mp3buf = mp3encoder.encodeBuffer(sampleChunk);
        if (mp3buf.length > 0) {
            mp3Data.push(mp3buf);
        }
    }

    // see if there's any data left
    var mp3buf = mp3encoder.flush();

    if (mp3buf.length > 0) {
        mp3Data.push(mp3buf);
    }

    // blob now contains an mp3 file
    var blob = new Blob(mp3Data, {type: 'audio/mp3'});
};

// take the blob from audioTrack
fileReader.readAsArrayBuffer(audioTrack.blob);

There is also blob.arrayBuffer but it's not fully supported:

https://developer.mozilla.org/en-US/docs/Web/API/Blob/arrayBuffer

This would give you the audioBuffer without using FileReader.