[Ffmpeg-devel] MP4: SBR in HE AAC - getting the right frequency?

Steve Lhomme steve.lhomme
Tue Jan 10 18:52:14 CET 2006

I already submitted a patch to do that for matroska but it was rejected 
because the code is already in faac (which is, again, only compiled in 
GPL mode). You can get that code and put it in libavutil so that codec 
and containers can use it.


Maxim wrote:
> Hi
> Who is good enough in implementing retreival of the right frequency from MP4 
> files with HE AAC? There is no checking for SBR currently implemented in 
> ffmpeg/libavformat/mov.c
> Or, alternatively, one can use FAAD2 to get this information, since it is 
> already implemented in it's libfaad/mp4.c file.
> All I know about SBR, is that you have to check for additional info in MP4 
> header on frequency or implicitly double all frequencies <= 24000 Hz if 
> there's no explicit SBR info. All MP4 files coming from Nokia SymbianOS 
> smartphones are with SBR, so converting them with ffmpeg produces twice 
> longer sound with half frequency.
> Currently I implemented dirty hack to double all frequencies that are 
> <=24000. It works for me, but I don't think it is right for all MP4 files 
> containing AAC.
> --
> lim
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