[FFmpeg-devel] [PATCH] lavc/hevcdec: HEVC decoder getting format clean up

[Hendrik Leppkes]

On Wed, Oct 24, 2018 at 5:09 PM Hendrik Leppkes <h.leppkes at gmail.com> wrote:
>
> On Wed, Oct 24, 2018 at 5:06 PM Jun Zhao <mypopydev at gmail.com> wrote:
> >
> > From: Jun Zhao <jun.zhao at intel.com>
> >
> > Add checking to avoid calling ff_thread_get_format repeatedly
> > whenever new slice header decoded.
> >
> > Signed-off-by: Lin Xie <lin.xie at intel.com>
> > Signed-off-by: Jun Zhao <jun.zhao at intel.com>
> > ---
> >  libavcodec/hevcdec.c |   17 +++++++++++------
> >  1 files changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
> > index a3b5c8c..16032a5 100644
> > --- a/libavcodec/hevcdec.c
> > +++ b/libavcodec/hevcdec.c
> > @@ -317,7 +317,6 @@ static void export_stream_params(AVCodecContext *avctx, const HEVCParamSets *ps,
> >      const HEVCWindow *ow = &sps->output_window;
> >      unsigned int num = 0, den = 0;
> >
> > -    avctx->pix_fmt             = sps->pix_fmt;
> >      avctx->coded_width         = sps->width;
> >      avctx->coded_height        = sps->height;
> >      avctx->width               = sps->width  - ow->left_offset - ow->right_offset;
> > @@ -357,7 +356,7 @@ static void export_stream_params(AVCodecContext *avctx, const HEVCParamSets *ps,
> >                    num, den, 1 << 30);
> >  }
> >
> > -static enum AVPixelFormat get_format(HEVCContext *s, const HEVCSPS *sps)
> > +static enum AVPixelFormat get_format(HEVCContext *s, const HEVCSPS *sps, int force_callback)
> >  {
> >  #define HWACCEL_MAX (CONFIG_HEVC_DXVA2_HWACCEL + \
> >                       CONFIG_HEVC_D3D11VA_HWACCEL * 2 + \
> > @@ -366,6 +365,8 @@ static enum AVPixelFormat get_format(HEVCContext *s, const HEVCSPS *sps)
> >                       CONFIG_HEVC_VIDEOTOOLBOX_HWACCEL + \
> >                       CONFIG_HEVC_VDPAU_HWACCEL)
> >      enum AVPixelFormat pix_fmts[HWACCEL_MAX + 2], *fmt = pix_fmts;
> > +    const enum AVPixelFormat *choices = pix_fmts;
> > +    int i;
> >
> >      switch (sps->pix_fmt) {
> >      case AV_PIX_FMT_YUV420P:
> > @@ -418,6 +419,11 @@ static enum AVPixelFormat get_format(HEVCContext *s, const HEVCSPS *sps)
> >      *fmt++ = sps->pix_fmt;
> >      *fmt = AV_PIX_FMT_NONE;
> >
> > +    if (!force_callback)
> > +        for (i = 0; choices[i] != AV_PIX_FMT_NONE; i++)
> > +            if (choices[i] == s->avctx->pix_fmt)
> > +                return choices[i];
> > +

Additionally, there can be a lot more properties that might result in
a different hwaccel selection, or even software fallback. Resolution,
frame rate, who knows what else.
The point of get_format is not only to determine the frame format, but
also notify the usercode / hwaccel about any changes in stream
properties.

If too many calls to get_format cause serious issues, then typically
the usercode that implements get_format is written badly. It should
verify that the current hwaccel is still capable of decoding the new
format, and only then act, instead of always re-creating the hardware
decoder. I realize that our avcodec code is also guilty of that, but
I've complained about that before, and thats the prime reason I also
don't use it. :)

- Hendrik