[FFmpeg-user] Differences in output between FFmpeg versions

[Ethan Coeytaux]

Hi Moritz,

Thank you for the response.  It's not 100% clear to me what the differences
are since it's decoded output, but when converting the same exact MP3 file
with different FFmpeg versions the decoded output files are different in
size and don't fully match up throughout the file.  For example on a test
MP3 file the decoded output using v2.2.1 had far more leading 0s than the
output from the v4.1.1 version.  Past that it mostly comes down to numerous
flipped bits throughout the files.  I'm not sure what "more correctly" is
in this context, and if one is more correct I would assume the latest
version is the most correct, but the outputs are undeniably different.

As for the consequences, I can't go into too much detail unfortunately, but
because we are trying to match songs and the first step is to decode the
audio it becomes far more difficult when the same exact song has different
decoded output depending on when it was decoded.

Would it be helpful if I posted the outputs of a decoded MP3 file?

-Ethan

On Tue, Oct 15, 2019 at 3:44 PM Moritz Barsnick <barsnick at gmx.net> wrote:

> On Tue, Oct 15, 2019 at 15:08:56 -0600, Ethan Coeytaux wrote:
>
> > When upgrading however we noticed there are substantial differences
> > in the output of FFmpeg when using a newer version (either 2.6.8,
> > 3.3.4, or 4.1.1) compared to the older version, which has notable
> > consequences on our analysis of the audio. However, the output from
> > 2.6.8, 3.3.4, and 4.1.1, while still different, are much more similar
> > than the output from 2.2.1.
> [...]
> > Any tips or advice would be much appreciated, thank you!
>
> You forgot to tell us what those differences in the output are. What
> are the "consequences on our analysis of the audio"?
>
> Are you saying audio was decoded (to raw) more correctly previously
> than it is now?
>
> I believe decoding of MP3 and AAC should be pretty precise. You can try
> alternative decoders (such as libfdk_aac) for comparison, but I'm
> riddled what you mean.
>
> Moritz
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