[FFmpeg-devel] [PATCH 1/2] lavu/pixfmt: add AYUV pixel format

[Carl Eugen Hoyos]

Am Sa., 31. Aug. 2019 um 19:25 Uhr schrieb Fu, Linjie <linjie.fu at intel.com>:
>
> > -----Original Message-----
> > From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
> > Of Mark Thompson
> > Sent: Saturday, August 31, 2019 23:10
> > To: ffmpeg-devel at ffmpeg.org
> > Subject: Re: [FFmpeg-devel] [PATCH 1/2] lavu/pixfmt: add AYUV pixel format
> >
> > On 31/08/2019 05:22, Fu, Linjie wrote:
> > >> -----Original Message-----
> > >> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On
> > Behalf
> > >> Of Carl Eugen Hoyos
> > >> Sent: Friday, August 30, 2019 00:12
> > >> To: FFmpeg development discussions and patches <ffmpeg-
> > >> devel at ffmpeg.org>
> > >> Subject: Re: [FFmpeg-devel] [PATCH 1/2] lavu/pixfmt: add AYUV pixel
> > format
> > >>
> > >> Am Do., 29. Aug. 2019 um 16:16 Uhr schrieb Fu, Linjie
> > <linjie.fu at intel.com>:
> > >>
> > >>> Thus AYUV will make more sense.
> > >>
> > >> If your hardware decoding does not produce valid alpha data (0xFF
> > >> for opaque, 0x00 for completely transparent), you cannot use an
> > >> FFmpeg pix_fmt that defines alpha for decoding.
> > >> If you define a pix_fmt that does not contain alpha information (as
> > >> needed for your hardware decoder), please do not use "A" in its
> > >> name.
> > >
> > > The hardware decode output is in packed 4:4:4:4 8 bit(32 bits in total). Apart>
> > from Y/U/V channel, there is an additional need for a channel to store the
> > > zero byte in surfaces(nb_components = 4). And it is designed in
> > hardware/driver
> > > for VA_FourCC_AYUV and AYUV format.
> > >
> > > It's not quite proper to use something like "0YUV" directly which indicates
> > that
> > > there is no Alpha channel data like"RGB0" or "0RGB"(nb_components = 3).
> > >
> > > "0YUV": YUV0/YUV0/...
> > > "RGB0":RGB/RGB/...
> >
> > I think you've misread what RGB0 is.  The component step is 4, not 3 (see
> > libavutil/pixdesc.c) - the format with a step of 3 is RGB24.
> >
> > RGBA:  R G B A R G B A ...
> > RGB0:  R G B 0 R G B 0 ...
> > RGB24: R G B R G B R G ...
>
> Thanks for pointing out this.
> Just took the nb_components into account and misread the step info at first.
>
> > Following the same pattern we would have:
> >
> > AYUV:  A Y U V A Y U V ...
> > 0YUV:  0 Y U V 0 Y U V ...
> >
> > To me it looks like 0YUV is exactly what you want here.
>
> Will update the patch if 0YUV is more acceptable.

Could you double-check if there is no bug in the decoder?
I ask because transparency is possible with hevc and the
relevant Windows format does support transparency from
how I read the specification.

Carl Eugen