Re: [FFmpeg-devel] [PATCH 3/3] libavutil/hwcontext_opencl: fix a bug for mapping qsv frame to opencl

[Soft Works <softworkz@hotmail.com>]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Mark
> Thompson
> Sent: Monday, December 27, 2021 7:51 PM
> To: ffmpeg-devel@ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH 3/3] libavutil/hwcontext_opencl: fix a bug
> for mapping qsv frame to opencl
> 
> On 16/11/2021 08:16, Wenbin Chen wrote:
> > From: nyanmisaka <nst799610810@gmail.com>
> >
> > mfxHDLPair was added to qsv, so modify qsv->opencl map function as well.
> > Now the following commandline works:
> >
> > ffmpeg -v verbose -init_hw_device vaapi=va:/dev/dri/renderD128 \
> > -init_hw_device qsv=qs@va -init_hw_device opencl=ocl@va -filter_hw_device
> ocl \
> > -hwaccel qsv -hwaccel_output_format qsv -hwaccel_device qs -c:v h264_qsv \
> > -i input.264 -vf "hwmap=derive_device=opencl,format=opencl,avgblur_opencl,
> \
> > hwmap=derive_device=qsv:reverse=1:extra_hw_frames=32,format=qsv" \
> > -c:v h264_qsv output.264
> >
> > Signed-off-by: nyanmisaka <nst799610810@gmail.com>
> > Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>
> > ---
> >   libavutil/hwcontext_opencl.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/libavutil/hwcontext_opencl.c b/libavutil/hwcontext_opencl.c
> > index 26a3a24593..4b6e74ff6f 100644
> > --- a/libavutil/hwcontext_opencl.c
> > +++ b/libavutil/hwcontext_opencl.c
> > @@ -2249,7 +2249,8 @@ static int opencl_map_from_qsv(AVHWFramesContext
> *dst_fc, AVFrame *dst,
> >   #if CONFIG_LIBMFX
> >       if (src->format == AV_PIX_FMT_QSV) {
> >           mfxFrameSurface1 *mfx_surface = (mfxFrameSurface1*)src->data[3];
> > -        va_surface = *(VASurfaceID*)mfx_surface->Data.MemId;
> > +        mfxHDLPair *pair = (mfxHDLPair*)mfx_surface->Data.MemId;
> > +        va_surface = *(VASurfaceID*)pair->first;
> >       } else
> >   #endif
> >           if (src->format == AV_PIX_FMT_VAAPI) {
> 
> Since these frames can be user-supplied, this implies that the user-facing
> API/ABI for AV_PIX_FMT_QSV has changed.
> 
> It looks like this was broken by using HDLPairs when D3D11 was introduced,
> which silently changed the existing API for DXVA2 and VAAPI as well.
> 
> Could someone related to that please document it properly (clearly not all
> possible valid mfxFrameSurface1s are allowed), and note in APIchanges when
> the API change happened?

Hi Mark,

QSV contexts always need to be backed by a child context, which can be DXVA2,
D3D11VA or VAAPI. You can create a QSV context either by deriving from one of
those contexts or when create a new QSV context, it automatically creates an
appropriate child context - either implicitly (auto mode) or explicitly, like
the ffmpeg implementation does in most cases.

When working with "user-supplied" frames on Linux, you need to create a VAAPI
context with those frames and derive a QSV context from that context.

There is no way to create or supply QSV frames directly. Looking at the code:

> *mfx_surface = (mfxFrameSurface1*)src->data[3];

A QSV frames context is using the mfxFrameSurface1 structure for describing 
the individual frames and mfxFrameSurface1 can only come from the MSDK runtime,
it cannot be user-supplied.

I don't think that there's something that needs to be documented because 
whatever user-side manipulation an API consumer would want to perform, it would
always need to derive the context either from QSV to D3D/VAAPI or from D3D to
VAAPI in order to access and manipulate individual frames. 

Kind regards,
softworkz



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