How to cut a Audio mp3 Blob in JS

Question

I have been looking to cut a audio blob in Js, and return a cut blob.

The blob is registered using WebAudioRecorder.js and using the mic of your pc.

I already found this repo: mp3-cutter, but it is written in node.js, and require to have access to the filesystem.

I also found this one: audio-cutter, but it has a UI.

I have explored multiple solution and did not find any simple solution.

While analyzing the recording, i found out that the mp3 registered with the mic have a 1024 bit header. Using this, and based on this, i wrote little Js function:

/**
 * params:
 *     params.src: Blob Object
 *     params.start: start time in sec
 *     params.end: end time in sec
 *     params.bitrate: in kbps
 */
function cutter(params) {
        let cuttedBlob;

        if (!params.src || params.start == null || params.end == null)
            throw 'Invalid parameters! ';
        
        if (params.start > params.end)
            throw 'Start is bigger than end! ';
        
        let kbps;
        if (!params.bitrate)
        {
            console.log("Checks have been done");
            console.log(params.src);
            var kbit = params.src.size / 128;
            console.log("bitrate: " + kbit);
            kbps= Math.ceil(Math.round(kbit / 204) / 16) * 16;
            console.log(kbps + "kbps");
        }
        else
            kbps = params.bitrate;
        
        cuttedBlob = params.src.slice(1024 + (params.start * kbps), params.end * kbps, "audio/mpeg3");
        return cuttedBlob;
}

But it does not seems to work.

I am missing something ?

Thanks in advance !

Does this answer your question? [Trim an audio file using javascript (first 3 seconds)](https://stackoverflow.com/questions/54303632/trim-an-audio-file-using-javascript-first-3-seconds) — I wrestled a bear once., Aug 25 '20 at 16:18
https://stackoverflow.com/questions/45662302/how-to-cut-an-audio-recording-in-javascript — I wrestled a bear once., Aug 25 '20 at 16:19
Yes, saw that answer, but isn't going to take to long to cut a 3mn audio ? — Lubenard, Aug 26 '20 at 12:29

score 3 · Accepted Answer · answered Sep 18 '20 at 12:41

3

Okay, i found out.

You need to convert your blob to ArrayBuffer, then to AudioBuffer, cut it, then reencode it using a encoder like mp3-lame-encoder-js

To help, i wrote a little library called simple-mp3-cutter

answered Sep 18 '20 at 12:41

Lubenard

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How to cut a Audio mp3 Blob in JS

1 Answers1