Re: [FFmpeg-devel] [PATCH 1/2] lavu/hwcontext_qsv: add support for AV_PIX_FMT_VUYX

[Philip Langdale <philipl@overt.org>]

On Mon, 5 Sep 2022 02:47:44 +0000
"Xiang, Haihao" <haihao.xiang-at-intel.com@ffmpeg.org> wrote:

> On Mon, 2022-08-29 at 14:01 +0000, Xiang, Haihao wrote:
> > On Mon, 2022-08-29 at 08:17 -0300, James Almer wrote:  
> > > On 8/29/2022 4:27 AM, Xiang, Haihao wrote:  
> > > > From: Haihao Xiang <haihao.xiang@intel.com>
> > > > 
> > > > AV_PIX_FMT_VUYX is used in FFmpeg for 8bit 4:4:4 content on
> > > > Intel HW, and MFX_FOURCC_AYUV is used in the SDK  
> > > 
> > > Sounds like you want the VUYA pixfmt instead.  
> > 
> > AV_PIX_FMT_VUYX is used for 4:4:4 content in the VAAPI path,
> > AV_PIX_FMT_VUYX is
> > expected when creating vaapi urface. QSV is based on 
> > VAAPI under Linux, so AV_PIX_FMT_VUYX is expected too in the QSV
> > path when creating vaapi surface.
> >   
> > >   
> > > > ---
> > > >   libavutil/hwcontext_qsv.c | 8 ++++++++
> > > >   1 file changed, 8 insertions(+)
> > > > 
> > > > diff --git a/libavutil/hwcontext_qsv.c
> > > > b/libavutil/hwcontext_qsv.c index 510f422562..a3350eae0f 100644
> > > > --- a/libavutil/hwcontext_qsv.c
> > > > +++ b/libavutil/hwcontext_qsv.c
> > > > @@ -119,6 +119,8 @@ static const struct {
> > > >                          MFX_FOURCC_YUY2 },
> > > >       { AV_PIX_FMT_Y210,
> > > >                          MFX_FOURCC_Y210 },
> > > > +    { AV_PIX_FMT_VUYX,
> > > > +                       MFX_FOURCC_AYUV },
> > > >   #endif
> > > >   };
> > > >   
> > > > @@ -1502,6 +1504,12 @@ static int map_frame_to_surface(const
> > > > AVFrame *frame,
> > > > mfxFrameSurface1 *surface)
> > > >           surface->Data.U16 = (mfxU16 *)frame->data[0] + 1;
> > > >           surface->Data.V16 = (mfxU16 *)frame->data[0] + 3;
> > > >           break;
> > > > +    case AV_PIX_FMT_VUYX:
> > > > +        surface->Data.V = frame->data[0];
> > > > +        surface->Data.U = frame->data[0] + 1;
> > > > +        surface->Data.Y = frame->data[0] + 2;
> > > > +        surface->Data.A = frame->data[0] + 3;  
> > > 
> > > This will go wrong with VUYX. You need to use AV_PIX_FMT_VUYA.  
> > 
> > frame->data[0] + 3 is valid even if alpha channel is ignored in
> > VUYX. Intel HW doesn't use the data in alpha channel actually, but
> > the SDK uses Microsoft pixel
> > format AYUV which is the alpha version, here set a valid address to
> > alpha channel when mapping a VUYX AVFrame to a AYUV mfx surface. 
> >   
> 
> Is there more comment about this patch ? 

Wouldn't it be more correct to fill the Data.A with 0xFF rather than
using the undefined value from the frame? I assume that the encoder
actually drops the value completely so it ultimately doesn't matter,
but it makes it clear that there is no alpha and if the encoder was to
start preserving it, it would preserve the desired value.

--phil
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