I have to export an AudioBuffer object to mp3 compressed file, in javascript, but the output has no sound.
lamejs is not outputting any audible sound: this is a duplicate, but no answer and I can't add a comment for ask if it's solved (need 50 reputation).
I use the same library, but I found a new maintained version, that fixes some bugs: https://github.com/shijinyu/lamejs
I can export the AudioBuffer in wav file. It works very well.
https://github.com/zhuker/lamejs/issues/68: here he says that encoder accepts PCM audio only. So I call getChannelData function (Web Audio API) from the AudioBuffer source.
// 2 channels
async encodeAudioBufferLame(audioBuffer) {
var mp3encoder = new Mp3Encoder(2, 44100, 128);
var mp3Data = [];
const [left, right] = [audioBuffer.getChannelData(0), audioBuffer.getChannelData(1)];
const sampleBlockSize = 1152; //can be anything but make it a multiple of 576 to make encoders life easier
for (var i = 0; i < left.length; i += sampleBlockSize) {
const leftChunk = left.subarray(i, i + sampleBlockSize);
const rightChunk = right.subarray(i, i + sampleBlockSize);
var mp3buf = mp3encoder.encodeBuffer(leftChunk, rightChunk);
if (mp3buf.length > 0) {
mp3Data.push(mp3buf);
}
}
var mp3buf = mp3encoder.flush(); //finish writing mp3
if (mp3buf.length > 0) {
mp3Data.push(mp3buf);
}
return mp3Data;
}
And then:
const mp3Data = await encodeAudioBufferLame(audioBuffer);
const blob = new Blob(mp3Data, {type: 'audio/mp3'});
const url = window.URL.createObjectURL(blob);
const downloadLink = document.createElement('a');
downloadLink.href = url;
downloadLink.setAttribute('download', `myAudio.mp3`);
downloadLink.click();
The output result has same original duration/length, but no sound. My sound card is good and the audio desktop is on.
I tried other libraries too, but I encountered other bugs.
All help is really appreciated!!
Great!! Thanks to James, who found a link with solution (see comment).
The solution:
async encodeAudioBufferLame(audioBuffer) {
var mp3encoder = new Mp3Encoder(2, audioBuffer.sampleRate, 128); // 44100 is replaced. It needs the real AudioBuffer sample rate. In my test case 48000.
var mp3Data = [];
const [left, right] = [audioBuffer.getChannelData(0), audioBuffer.getChannelData(1)];
// The transformed data, this is what you will pass to lame instead
// If you are sure to use a Float32Array you can skip this and use [left, right] const.
const l = new Float32Array(left.length);
const r = new Float32Array(right.length);
//Convert to required format
for(var i=0;i<left.length;i++) {
l[i] = left[i]*32767.5;
r[i] = right[i]*32767.5;
}
const sampleBlockSize = 1152; //can be anything but make it a multiple of 576 to make encoders life easier
for (var i = 0; i < l.length; i += sampleBlockSize) {
const leftChunk = l.subarray(i, i + sampleBlockSize);
const rightChunk = r.subarray(i, i + sampleBlockSize);
var mp3buf = mp3encoder.encodeBuffer(leftChunk, rightChunk);
if (mp3buf.length > 0) {
mp3Data.push(mp3buf);
}
}
var mp3buf = mp3encoder.flush(); //finish writing mp3
if (mp3buf.length > 0) {
mp3Data.push(mp3buf);
}
return mp3Data;
}
Thanks a lot James!!
I can't vote your comment, maybe for my poor reputation.