[FFmpeg-devel] [PATCH] libavcodec/vp8dec: fix the multi-thread HWAccel decode error

[mypopy at gmail.com]

On Fri, Sep 21, 2018 at 12:08 PM Xiang, Haihao <haihao.xiang at intel.com> wrote:
>
> On Thu, 2018-08-09 at 15:09 +0800, Jun Zhao wrote:
> > the root cause is update_dimentions call get_pixel_format will
>
> Typo? s/dimentions/dimensions. And I see the same typo a few times in this log.
>
Ha, a good catch.

> > trigger the hwaccel_uninit/hwaccel_init , in current context,
>
> What is the decode error? Could you document the error a little or a link to the
> issue?
>
In mutil-thread decoding case with media-driver, Vp8 HWaccel decoder
will carsh in some case.

> > there are 3 situations in the update_dimentions():
> > 1. First time calling. No matter single thread or multithread,
> >    get_pixel_format() should be called after dimentions were
> >    set;
> > 2. Dimention changed at the runtime. Dimention need to be
> >    updated when macroblocks_base is already allocated,
>
> According to the code, ff_set_dimensions is called to overwrite previously setup
> dimensions when height is changed no matter
> s->macroblocks_base is allocated or not. I think the HW frames and context
> should be re-created as well for this case
>
> But I am curious why height and width are treated differently in this condition:
>
>     if (width  != s->avctx->width || ((width+15)/16 != s->mb_width ||
> (height+15)/16 != s->mb_height) && s->macroblocks_base ||
>         height != s->avctx->height) {
>        ...
>        ff_set_dimensions(...);
> }
>
> The condition for updating dimensions is simple in VP9:
Now I didn't test VP9 decoder in this case
>
>    if (!(s->pix_fmt == s->gf_fmt && w == s->w && h == s->h)) {
>        ff_set_dimensions(...);
>        ...
>    }
>
> >    get_pixel_format() should be called to recreate new frames
> >    according to updated dimention;
> > 3. Multithread first time calling. After decoder init, the
> >    other threads will call update_dimentions() at first time
> >    to allocate macroblocks_base and set dimentions.
> >    But get_pixel_format() is shouldn't be called due to low
> >    level frames and context are already created.
> > In this fix, we only call update_dimentions as need.
> >
> > Signed-off-by: Wang, Shaofei <shaofei.wang at intel.com>
> > Reviewed-by: Jun, Zhao <jun.zhao at intel.com>
> > ---
> >  libavcodec/vp8.c |    7 +++++--
> >  1 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavcodec/vp8.c b/libavcodec/vp8.c
> > index 3adfeac..18d1ada 100644
> > --- a/libavcodec/vp8.c
> > +++ b/libavcodec/vp8.c
> > @@ -187,7 +187,7 @@ static av_always_inline
> >  int update_dimensions(VP8Context *s, int width, int height, int is_vp7)
> >  {
> >      AVCodecContext *avctx = s->avctx;
> > -    int i, ret;
> > +    int i, ret, dim_reset = 0;
> >
> >      if (width  != s->avctx->width || ((width+15)/16 != s->mb_width ||
> > (height+15)/16 != s->mb_height) && s->macroblocks_base ||
> >          height != s->avctx->height) {
> > @@ -196,9 +196,12 @@ int update_dimensions(VP8Context *s, int width, int
> > height, int is_vp7)
> >          ret = ff_set_dimensions(s->avctx, width, height);
> >          if (ret < 0)
> >              return ret;
> > +
> > +        dim_reset = (s->macroblocks_base != NULL);
>
>
> >      }
> >
> > -    if (!s->actually_webp && !is_vp7) {
> > +    if ((s->pix_fmt == AV_PIX_FMT_NONE || dim_reset) &&
> > +         !s->actually_webp && !is_vp7) {
> >          s->pix_fmt = get_pixel_format(s);
> >          if (s->pix_fmt < 0)
> >              return AVERROR(EINVAL);