[FFmpeg-devel] [PATCH 2/2] lavc/vp9: support hardware decode with resolution changing on inter frame

[Fu, Linjie]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Hendrik Leppkes
> Sent: Friday, December 27, 2019 18:22
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH 2/2] lavc/vp9: support hardware
> decode with resolution changing on inter frame
> 
> On Fri, Dec 27, 2019 at 9:59 AM Linjie Fu <linjie.fu at intel.com> wrote:
> >
> > VP9 decoder should be able to handle resolution changing on inter
> > frame without re-initialization. For hardware decoder, re-allocate hardware
> > frame surface.
> >
> > Fix #8068 for VA-API.
> >
> > Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> > ---
> > Request for comments.
> > This works for VA-API, however for dxva2 it didn't cover all cases.
> >
> > Another idea is to register a call-back function in AVHWAccel (such as
> > ff_vp9_dxva2_hwaccel) to handle surface re-allocation according to
> > the hardware decoder.
> >
> >  libavcodec/vp9.c | 18 ++++++++++++++----
> >  1 file changed, 14 insertions(+), 4 deletions(-)
> >
> > diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c
> > index 0fd15ef..a7b4c6a 100644
> > --- a/libavcodec/vp9.c
> > +++ b/libavcodec/vp9.c
> > @@ -34,6 +34,7 @@
> >  #include "vp9dec.h"
> >  #include "libavutil/avassert.h"
> >  #include "libavutil/pixdesc.h"
> > +#include "decode.h"
> >
> >  #define VP9_SYNCCODE 0x498342
> >
> > @@ -220,11 +221,20 @@ static int update_size(AVCodecContext *avctx,
> int w, int h)
> >          *fmtp++ = s->pix_fmt;
> >          *fmtp = AV_PIX_FMT_NONE;
> >
> > -        ret = ff_thread_get_format(avctx, pix_fmts);
> > -        if (ret < 0)
> > -            return ret;
> > +        if (avctx->internal->hwaccel_priv_data && s->pix_fmt == s->gf_fmt
> && (s->w != w || s->h != h)) {
> > +            const AVHWDeviceContext *device_ctx =
> > +                (AVHWDeviceContext*)avctx->hw_device_ctx->data;
> > +            ret = ff_decode_get_hw_frames_ctx(avctx, device_ctx->type);
> > +            if (ret < 0)
> > +                return ret;
> > +        } else {
> > +            ret = ff_thread_get_format(avctx, pix_fmts);
> > +            if (ret < 0)
> > +                return ret;
> > +
> > +            avctx->pix_fmt = ret;
> > +        }
> >
> > -        avctx->pix_fmt = ret;
> >          s->gf_fmt  = s->pix_fmt;
> >          s->w = w;
> >          s->h = h;
> 
> hwaccels are not guaranteed to have a hw_frames ctx, and avcodec is
> not guaranteed to manage the surfaces it decodes to at all (they could
> be shared with eg. a renderer and allocated externally), as such a

Thanks, and would you please help to share more information about how to reproduce?
1. no hw_frame_ctx, only hw_device_ctx
2. surfaces shared with a rendered and allocated externally
(externally provided hw_frames_ctx)

I'd like to step into these and try to find a proper/general solution.

> decoder really can't reliably re-allocate this itself - thats what the
> get_format callback is for, which informs the user that new dimensions
> are required.

It's vp9 (and AV1) specific, so I didn't intend to modify in the general path(ff_get_format) firstly.

Instead of fixing in codec(update_size() in vp9.c),  if we are going to handle this in user
(ff_get_format() in decode.c) to manage the surface, IMHO a modification in API may be needed
to register a reinit function in AVHWAccel.
See:
https://github.com/intel-media-ci/ffmpeg/pull/153

thx

- linjie