[FFmpeg-devel] The v4l2 demuxer and the use of libv4l2

Clément Bœsch ubitux at gmail.com
Mon Dec 31 01:53:47 CET 2012

On Sun, Dec 30, 2012 at 01:48:10PM +0000, Carl Eugen Hoyos wrote:
> Stephan Hilb <stephan <at> ecshi.net> writes:
> > To my surprise I noticed just now that when ffmpeg is build with the
> > "--enable-libv4l2" flag (and thereby using libv4l2 as an additional
> > layer between ffmpeg and the kernel api) my camera doesn't work as
> > expected and the cpia decoder isn't used (libv4l2 does the conversion
> > instead).
> > 
> > Now this leads me to the question why the libv4l2 userspace library is
> > used anyways when there is an appropriate decoder available for the
> > format (cpia in my case).
> Users requested this repeatedly (although I cannot remember 
> a good reason). It would mean additional programming effort 
> to make it configurable at runtime.

Yes, it was a bit more complex to make it configurable at runtime. Patch
are welcome. Also note that you can make use of LD_PRELOAD instead of the

  LD_PRELOAD=/usr/lib/libv4l/v4l2convert.so ./ffmpeg -f v4l2 -i ...

Clément B.
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