[FFmpeg-user] Conversion wav -> mp3 -> wav

[Erik Dobberkau]

Am Donnerstag, 22. Juni 2017 schrieb Rodolfo Medina :

> Hi all.
>
> As an experiment, I converted a .wav file to mp3 format and then back into
> wav
> again, just to see what happens:
>
>  $ ffmpeg -i file1.wav file1.mp3
>  $ ffmpeg -i file1.mp3 file2.wav
>
> I've always heard and read that the first step produces a loss in
> quality.  So
> I would expect that to be seen in a reduction of size.  Instead, I was
> suprised
> to see that file1.wav and file2.wav are both 154M large.  Also the output
> of
> `ffmpeg -i' is almost the same for the two: in both cases, there is:
>
>  Duration: 00:15:10.84, bitrate: 1411 kb/s
>     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz,
> stereo, s16, 1411 kb/s
>
> So I wonder, and am asking to you listers, in where that quality loss is
> shown
> and how it can be detected.  Or maybe should we think and conclude that the
> original quality is restored with the second step...?
>
>
>
Hi Rodolfo,

please read here:
a)  https://en.m.wikipedia.org/wiki/Pulse-code_modulation
b) https://en.m.wikipedia.org/wiki/MP3

You're going from a to b and back from b to a. Mathematically you should
get the result you're getting, however audio quality, or fidelity is being
compromised due to the application of several data reduction and
compression methods. If you phase invert file2.wav and add it to file1.wav
you will have a difference.

Best,
Erik