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

[Jorge Ramirez-Ortiz]

On 09/20/2017 08:31 PM, wm4 wrote:
> 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.)

ok.

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

I see. I'll find out what is the process to modify the API and why the current 
drivers don't use it.
Notice that -even if the API change is accepted in the coming months - all the 
drivers currently available in the field wont be using it in the near future 
though (they will be returning a default, null I guess).

I just dont have any control on the drivers or the API itself: do you think this 
will be blocking the upstream process?

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