Re: [FFmpeg-devel] [PATCH] lavc/vp9: set update_map to 0 when segmentation.enabled is 0

[Lynne via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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On 22/05/2024 18:17, Philip Langdale via ffmpeg-devel wrote:
> On Wed, 22 May 2024 11:10:31 -0400
> "Ronald S. Bultje" <rsbultje@gmail.com> wrote:
> 
>> Hi,
>>
>> On Wed, May 22, 2024 at 10:36 AM Hendrik Leppkes <h.leppkes@gmail.com>
>> wrote:
>>
>>> On Thu, Feb 29, 2024 at 7:19 AM llyyr <llyyr@yukari.in> wrote:
>>>>
>>>> segmentation.update_map is never reset to 0 on a new frame, and
>>>> retains the value from the previous frame. This bugs out a bunch
>>>> of hwaccel drivers when segmentation.enabled is 0 but update_map
>>>> isn't because they don't ignore values behind switches. We also
>>>> do this for vp8* so this commit is just mirroring the vp8 logic.
>>>>
>>>> This fixes an issue with certain samples** that causes blocky
>>>> artifacts with vaapi and d3d11va (as far as known hwaccel drivers
>>>> go). Mesa worked around*** this by ignoring this field if
>>>> segmentation.enabled is 0, but d3d11va still doesn't work.
>>>>
>>>> *
>>> https://git.ffmpeg.org/gitweb/ffmpeg.git/blob/HEAD:/libavcodec/vp8.c#l811
>>>   
>>>> ** https://github.com/mpv-player/mpv/issues/13533
>>>> ***
>>>> https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27816
>>>>
>>>> Signed-off-by: llyyr <llyyr@yukari.in>
>>>> ---
>>>>   libavcodec/vp9.c | 2 ++
>>>>   1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c
>>>> index 855936cdc1c7..4a628625131e 100644
>>>> --- a/libavcodec/vp9.c
>>>> +++ b/libavcodec/vp9.c
>>>> @@ -717,6 +717,8 @@ static int decode_frame_header(AVCodecContext
>>>> *avctx, s->s.h.segmentation.feat[i].skip_enabled =
>>> get_bits1(&s->gb);
>>>>               }
>>>>           }
>>>> +    } else {
>>>> +        s->s.h.segmentation.update_map = 0;
>>>>       }
>>>>
>>>>       // set qmul[] based on Y/UV, AC/DC and segmentation Q idx
>>>> deltas
>>>>
>>>> base-commit: d263fce2b209e86a5a1e8f1b6aa33430ecc2c187
>>>> --
>>>
>>> Change LGTM.
>>> I was debugging the same issue today, and found the same problem
>>> with some hwaccels not properly ignoring update_map when
>>> segmentation is disabled.
>>>
>>> Will apply soon if there are no further comments.
>>>   
>>
>> Is fine, please apply.
>>
> 
> Another LGTM. We've been seeing this reported on the mpv side as well.
> 
> --phil
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Can't this get fixed by hwaccel code rather than globally?
I'd hate to apply fixes with no information in shared code. This can get 
removed with no information about what relies on it.

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