I am using Recorder.js to record audio from mic. That library can encode the PCM data in WAV and I can successfully play it back using <audio>. But, the resulting WAV data is too huge (~38MB for a 5 minute recording). I tried using libmp3lame.js available from Speech-to-Server.

In recorderWorker.js, I am importing the Lame script:

importScripts(libmp3lame.js);

Then, I changed the exportWAV() function to encode the PCM buffers into MP3 instead of WAV.

function exportWAV(type){

    var bufferL = mergeBuffers(recBuffersL, recLength);

    var bufferR = mergeBuffers(recBuffersR, recLength);

    //var interleaved = interleave(bufferL, bufferR);



    console.log(Start MP3 encoding);

    var mp3codec = Lame.init();

    Lame.set_mode(mp3codec, Lame.JOINT_STEREO);

    Lame.set_num_channels(mp3codec, 2);

    Lame.set_out_samplerate(mp3codec, sampleRate);

    Lame.set_bitrate(mp3codec, 128);

    Lame.init_params(mp3codec);



    var mp3data = Lame.encode_buffer_ieee_float(mp3codec, bufferL, bufferR);

    audioBlob = new Blob([mp3data.data], { type: audio/mp3 });

    console.log(Done MP3 encoding);



    this.postMessage(audioBlob);

}

But, the Lame.encode_buffer_ieee_float method is throwing this error:

Uncaught RangeError: Invalid array buffer length 

Here PCM data in bufferL and bufferR are Float32Array. I can not find out what exactly Lame.encode_buffer_ieee_float expects as input.

The offending line in Lame.encode_buffer_ieee_float that is throwing the error is:

var arraybuf = new ArrayBuffer(nread);

I put a breakpoint and checked the value of nread. It is -1.

So, my question is how do I use the Lame MP3 JavaScript library in this situation? Thank you.