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

[Carl Eugen Hoyos]

2019-03-06 9:25 GMT+01:00, Wang, Shaofei <shaofei.wang at intel.com>:
>> -----Original Message-----
>> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of
>> Carl Eugen Hoyos
>> Sent: Wednesday, March 6, 2019 3:49 PM
>> To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
>> Subject: Re: [FFmpeg-devel] [PATCH] libavcodec/vp8dec: fix the
>> multi-thread
>> HWAccel decode error
>>
>> 2018-08-09 9:09 GMT+02:00, Jun Zhao <mypopydev at gmail.com>:
>> > the root cause is update_dimentions call get_pixel_format will trigger
>> > the hwaccel_uninit/hwaccel_init , in current context, 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,
>> >    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) {
>>
>> Why is the new variable dim_reset needed?
>> Wouldn't the patch be simpler if you used s->macroblocks_base here?
> Since dim_reset was set in the "if" segment, it equal to
> (width != s->avctx->width || ((width+15)/16 != s->mb_width ||
> (height+15)/16 != s->mb_height) || height != s->avctx->height) &&
> s->macroblocks_base

Thank you!

Carl Eugen