Re: Wav to Mp3 leads to an mp3 file that has a longer duration

Martin Ratinaud <[email protected]> writes:

> Hi all,
>
> I'm converting a file called vocals.wav to vocals.mp3
>  vocals.wav
> <https://drive.google.com/file/d/1he1eCJag1G8iGkgL932jy_mXuLT_khGM/view?usp=drive_web>
> For this I'm using this command
>
> ```
> sox vocals.wav vocals.mp3
> ```
> and here is the result of the corresponding files
>
> - original file
> ```
> soxi /Users/martin/Downloads/split-test/vocals.wav
>
> Input File     : '/Users/martin/Downloads/split-test/vocals.wav'
> Channels       : 2
> Sample Rate    : 44100
> Precision      : 16-bit
> Duration       : 00:03:00.00 = 7938000 samples = 13500 CDDA sectors
> File Size      : 31.8M
> Bit Rate       : 1.41M
> Sample Encoding: 16-bit Signed Integer PCM
> ```
>
> - converted file
> ```
> soxi /Users/martin/Downloads/split-test/vocals.mp3
>
> Input File     : '/Users/martin/Downloads/split-test/vocals.mp3'
> Channels       : 2
> Sample Rate    : 44100
> Precision      : 16-bit
> Duration       : 00:03:00.04 = 7939544 samples = 13502.6 CDDA sectors
> File Size      : 2.88M
> Bit Rate       : 128k
> Sample Encoding: MPEG audio (layer I, II or III)
> ```
>
> You can see that the duration is not the same which is weird and the number
> of samples also changed.
> In fact, 1544 samples have been added to the beginning of the file
>
> If I try to launch `sox -V vocals.mp3 vocals-trimmed.mp3 trim 1544s` it
> does not work

MP3 files have to have a multiple of 1152 samples.  This can't be
avoided.  If the input isn't such a multiple, it will be padded by the
encoder.

-- 
Måns Rullgård