[Libav-user] [Audacity-devel] Requesting help to port Audacity to recent FFmpeg

Michael Niedermayer michaelni at gmx.at
Sat May 24 17:44:21 CEST 2014

On Fri, May 23, 2014 at 11:23:17PM +0200, Benjamin Drung wrote:
> Hi Michael,
> Am Mittwoch, den 21.05.2014, 02:16 +0200 schrieb Michael Niedermayer:
> > > I like to commit your
> > > work to the Audacity SVN so that we have both - support for FFmpeg and
> > > Gstreamer.
> > 
> > that sounds great
> I committed your code to the Audacity SVN with your name in
> Signed-off-by, because I failed to find a git-am equivalent to preserve
> the committer and date. Thanks for your work.
> While committing, I made some small indentation adjustments. Audacity
> uses 3 spaces for indentation and some of your changes used 4 spaces. I
> merged your debug fprintf removal into the respective commit. I also
> committed my libav 9 support patch.
> > > 2) I can't export audio as mp4. Neither as mp4 export, nor as custom
> > > FFmpeg export (can't be selected there). FFmpeg has mp4 support enabled:
> > > 
> > > $ ffmpeg -formats 2>/dev/null | grep mp4
> > >  D  mov,mp4,m4a,3gp,3g2,mj2 QuickTime / MOV
> > >   E mp4             MP4 (MPEG-4 Part 14)
> > 
> > hmmm, what do you mean by "mp4" ?
> > there are alot of audio codecs that can be stored in mp4, for example
> > aac, mp3, vorbis, also there are multiple ways to encode aac, libfaac
> > ffmpegs native encoder and a few others ...
> > 
> > I tried a few things and found a few bugs (which i fixed) but iam
> > not convinced i fixed the issue you describe
> Sorry. My description was imprecise and incorrectly (m4a instead of
> mp4). I was talking about File -> Export Audio... -> "M4A (AAC) Files
> (FFmpeg)". When selecting this format, the exported file has 0 bytes
> content. Selecting "Custom FFmpeg Export" and then "mp4" format and
> "aac" codec, the result will be the same (empty exported file).X

This is likely due to AVCodecContext.strict_std_compliance not being
set so as to allow experimental encoders and your installed
ffmpeg/libavcodec not being build with any non experimental aac

Theres probably a error printed to the log that indicates if its that
or something else.

not sure which is the preferred way to fix this, maybe adding a
way to the GUI to allow the user to set the value for
strict_std_compliance. Or possibly to always set it so experimental
codecs are used when selected ...

>  The same
> applies for the wav format with pcm_s16le codec.

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
of college or go to community college in order to be able to afford
settlements. -- The RIAA
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