Re: [FFmpeg-devel] [PATCH v1 1/9] lavu/pix_fmt: add P012 pixel format

["Xiang, Haihao" <haihao.xiang-at-intel.com@ffmpeg.org>]

On Sun, 2022-01-23 at 01:06 +0100, Carl Eugen Hoyos wrote:
> Am Fr., 21. Jan. 2022 um 06:56 Uhr schrieb Xiang, Haihao
> <haihao.xiang-at-intel.com@ffmpeg.org>:
> > 
> > > -----Original Message-----
> > > From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Xiang,
> > > Haihao
> > > Sent: Tuesday, June 30, 2020 15:34
> > > To: ffmpeg-devel@ffmpeg.org
> > > Subject: Re: [FFmpeg-devel] [PATCH v1 1/9] lavu/pix_fmt: add P012 pixel
> > > format
> > > 
> > > > Am So., 28. Juni 2020 um 23:01 Uhr schrieb Mark Thompson <sw@jkqxz.net>:
> > > > 
> > > > > FFmpeg has always used pixfmt as defining both the memory layout
> > > > > and which bits are used in that (so, for example, ARGB and 0RGB
> > > > > are not the same thing)
> > > > 
> > > > But they have the same bitdepth per component...
> > > Agree with Mark. P012 and P016 have different significant bits, we should
> > > use
> > > different pixfmts, otherwise an extra field in AVFrame is needed for bit
> > > depth.
> > > 
> > > BTW there are the YUV420P variants for 10 / 12 / 14 / 16 bit in FFmpeg, it
> > > would be better to follow FFmpeg's style to introduce P012 format instead
> > > of reusing P016.
> 
> I was under the impression that YUV420P12 is much more different from
> YUV420P16 than P012 from P016: Did I misunderstand?
> (Reading the thread again, I don't think I did)

I understand YUV420P12 is a LSB format, so YUV420P12 can't be taken
as YUV420P16. The style here means FFmpeg uses pixfmt for both memory layout and
bit depth. 

> 
> > Sorry for picking up this old thread.
> > 
> > We'd like to add the support for 12bit decoding / encoding in VAAPI and QSV.
> > Is there any other concern if adding P012 in FFmpeg ?
> 
> Did you already explain why you cannot use P016 or in which situation
> it would create a different output?

$ ffmpeg -hwaccel vaapi -f rawvideo -pix_fmt p016 -s 1920x1080 -i input.yuv -vf
"hwupload,format=vaapi" -c:v hevc_vaapi -f null -

If using P016, how will we know the input is 12bit indeed, not 14/16bit if
hevc_vaapi may support both 12bit and 14/16bit inputs in the future ? Will we
add a new option to ffmpeg to specify the bit depth and a new flag in AVFrame ?

Thanks
Haihao

> 
> Carl Eugen
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