Re: [FFmpeg-devel] [PATCH] lavc/vvc: AVERROR_PATCHWELCOME for subpictures

[Nuo Mi <nuomi2021@gmail.com>]

On Tue, Mar 12, 2024 at 5:09 PM Frank Plowman <post@frankplowman.com> wrote:

> On 12/03/2024 03:33, Wang, Fei W wrote:
> > On Mon, 2024-03-11 at 21:57 -0300, James Almer wrote:
> >> On 3/11/2024 9:49 PM, Michael Niedermayer wrote:
> >>> On Mon, Mar 11, 2024 at 06:53:31PM +0000, Frank Plowman wrote:
> >>>> VVC's subpictures feature is not yet implemented in the native
> >>>> decoder.
> >>>> Throw an AVERROR_PATCHWELCOME when trying to decode a bitstream
> >>>> using
> >>>> the feature.  Fixes crashes when trying to decode bitstreams
> >>>> which
> >>>> use the feature.
> >>>>
> >>>> Signed-off-by: Frank Plowman <post@frankplowman.com>
> >>>> ---
> >>>>   libavcodec/vvc/vvc_ps.c | 15 +++++++++++++++
> >>>>   1 file changed, 15 insertions(+)
> >>>
> >>> This breaks fate-vvc-conformance-SUBPIC_A_3
> >>>
> >>> make fate-vvc-conformance-SUBPIC_A_3
> >>> TEST    vvc-conformance-SUBPIC_A_3
> >>> --- ./tests/ref/fate/vvc-conformance-SUBPIC_A_3     2024-03-05
> >>> 02:37:36.235300141 +0100
> >>> +++ tests/data/fate/vvc-conformance-SUBPIC_A_3      2024-03-12
> >>> 01:47:27.301593567 +0100
> >>> @@ -1,9 +0,0 @@
> >>> -#tb 0: 1/25
> >>> -#media_type 0: video
> >>> -#codec_id 0: rawvideo
> >>> -#dimensions 0: 1920x1080
> >>> -#sar 0: 0/1
> >>> -0,          0,          0,        1,  6220800, 0xa419cfb6
> >>> -0,          1,          1,        1,  6220800, 0xa419cfb6
> >>> -0,          2,          2,        1,  6220800, 0xa419cfb6
> >>> -0,          3,          3,        1,  6220800, 0xa419cfb6
> >>> Test vvc-conformance-SUBPIC_A_3 failed. Look at
> >>> tests/data/fate/vvc-conformance-SUBPIC_A_3.err for details.
> >>> tests/Makefile:318: recipe for target 'fate-vvc-conformance-
> >>> SUBPIC_A_3' failed
> >>> make: *** [fate-vvc-conformance-SUBPIC_A_3] Error 69
> >>>
> >>> thx
> >>
> >> The sample appears to decode fine and doesn't crash, although all
> >> four
> >> frames are exactly the same (I don't know is that's intended).
> >
> > The result is correct. Assume native decode can handle subpic, at least
> > a part of the feature.
> >
> >> Maybe the crashes can be fixed in some other form? And abort only if
> >> FF_COMPLIANCE_STRICT is requested.
> >
> > Previous I made a patch to fix the crash in setup ps, but still get
> > error in decoding slice, it's better to return AVERROR_PATCHWELCOME
> > only in case of pps_single_slice_per_subpic_flag.
> >
> > https://github.com/intel-media-ci/ffmpeg/pull/723
> >
> > Thanks
> > Fei
>
> Hi,
>
> Thanks all for your reviews.
>
> Yes, the feature is most problematic if pps_single_slice_per_subpic_flag
> is 1.  This is because there is some unimplemented logic in the
> parameter set parser in this case which leads to some out-of-bounds
> accesses.  Subpictures will also fail to decode bitexact if
> sps_independent_subpics is 1, although in practice the distortion this
> introduces is fairly subtle.  I think we are able to decode other
> subpicture bitstreams bitexact.  SUBPIC_A_HUAWEI_3 falls into this last
> category.
>
> I posted a patch, like yours Fei, which errors only the most problematic
> pps_single_slice_per_subpic_flag bitstreams some time ago:
>
> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20240201140055.63805-1-post@frankplowman.com/
> and the feedback I received there was to make this patch.  I have also
> implemented the logic needed for pps_single_slice_per_subpic_flag here:
> https://github.com/ffvvc/FFmpeg/pull/191.  I would be happy to make a v2
> of the pps_single_slice_per_subpic_flag patch which moves where the
> error is being returned, or to put the GitHub PR on the ML if people
> would rather one of those two alternatives.
>
Hi Frank and all,
Thank you for the patch and review.
I have a local patch for subpic, hope I can make all clips passed and send
out patches in the following 1~2 weeks.

>
> Thanks again,
> --
> Frank
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