[FFmpeg-devel] [PATCHv12] libavcodec: v4l2: add support for v4l2 mem2mem codecs

wm4 nfxjfg at googlemail.com
Thu Sep 21 06:31:30 EEST 2017

On Wed, 20 Sep 2017 19:01:52 -0700
Jorge Ramirez-Ortiz <jorge.ramirez-ortiz at linaro.org> wrote:

> > Btw. I noticed that this apparently never sets chroma_location?  
> I didnt find anything in v4l2 to retrieve the chroma_location from the kernel 
> driver (the API doesnt handle this information).
> does ffmpeg need this field and if so, can it be retrieved from somewhere else 
> (bitstream perhaps)?

Yes, chroma location matters. Some users notice if the location is
incorrect. It can be retrieved from the bitstream, but that would
require you to parse it. Which probably would require additional code.
(You can't rely on the pre-filled parameters by libavformat, because an
API user doesn't have to use libavformat.)

I suggest you make the kernel devs add this parameter. There might be
more such missing parameters, I noticed this one only by chance.

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