mp3 is half tempo and bad quality about lamejs HOT 6 CLOSED

Looks like you encode stereo as mono

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On Jun 21, 2016, at 00:56, Julius Athenstaedt [email protected] wrote:

First of all thank you for that great lib!

I want to convert a 1411 kbps pcm_s16le 44100 Hz stereo, s16(recorded with recordRTC) to mp3.
The problem is that the wav file sounds perfect but the converted mp3 file sounds bad, sounds lower than the original and is twice as long.

Full js: http://julius.athenstaedt.net/rep/rcx2/background.js
recorded wav: http://julius.athenstaedt.net/rep/wav%20(16).wav
converted mp3 http://julius.athenstaedt.net/rep/mpeg%20(14).mp3

function convertToMP3(audioBlob) {
//audioBlob is the recorded Blob from recordRTC api
//with FileReader get the dataform like with XMLHttpRequest (maybe the problem?)
console.log(audioBlob);
var audioData;
fileReader = fileReader || new FileReader();
fileReader.onload = function() {
audioData = this.result;

            var wav = lamejs.WavHeader.readHeader(new DataView(audioData));
            console.log("wav:",wav);
            mp3encoder = new lamejs.Mp3Encoder(wav.channels, wav.sampleRate, 128);
            var mp3Data = [];

            left = new Int16Array(audioData, wav.dataOffset, wav.dataLen /2); 
            right = new Int16Array(audioData, wav.dataOffset, wav.dataLen /2); 

            sampleBlockSize = 1152; 

            var mp3buf=[];
            for (var i = 0; i < left.length; i += sampleBlockSize) {
                leftChunk = left.subarray(i, i + sampleBlockSize);
                rightChunk = right.subarray(i, i + sampleBlockSize);
                mp3buf = mp3encoder.encodeBuffer(leftChunk, rightChunk);
                if (mp3buf.length > 0) {
                    mp3Data.push(new Int8Array(mp3buf));
                }
            }
            mp3buf = mp3encoder.flush(); //finish writing mp3

            if (mp3buf.length > 0) {
                mp3Data.push(new Int8Array(mp3buf));
            }

            var blob = new Blob(mp3Data, {
                type: 'audio/mp3'
            });
            var url = window.URL.createObjectURL(blob);
    saveFile(url, "mpeg.mp3");
};
fileReader.readAsArrayBuffer(audioBlob);

}
Thank You for help!!
(sorry for bad english)

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And what I have to change? I have used the code for stereo from the example.

from lamejs.

Did you split your stereo input into left and right channels?

Sent from my iPhone

On Jun 24, 2016, at 18:34, Julius Athenstaedt [email protected] wrote:

And what I have to change? I have used the code for stereo from the example.

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from lamejs.

Yes like in the example, but their was only one second silence. So maybe I splitted wrong:

left = new Int16Array(audioData, wav.dataOffset, wav.dataLen /2); 
right = new Int16Array(audioData, wav.dataOffset, wav.dataLen /2); 

from lamejs.

Yes this is wrong.
Split by taking every other sample into separate channel.
For i=0 i<data.length i+=2
Left= data [i]
Right = data[i+1]

And then put left and right samples into their own int16 arrays

Sent from my iPhone

On Jun 24, 2016, at 19:18, Julius Athenstaedt [email protected] wrote:

Yes like in the example, but their was only one second silence. So maybe I splitted wrong:

left = new Int16Array(audioData, wav.dataOffset, wav.dataLen /2);
right = new Int16Array(audioData, wav.dataOffset, wav.dataLen /2);
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from lamejs.

Thank you that was the error.
correctly splitted:

//audioData is the wav-blob converted to an ArrayBuffer
var data = new Int16Array(audioData, wav.dataOffset, wav.dataLen/2);

 for (i = 0; i < data.length; i += 2) {
         left.push(data[i]);
         right.push(data[i + 1]);
}

left = new Int16Array(left);
right = new Int16Array(right);

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