[x264-devel] Corrupted slices

[BugMaster]

On Wed, 11 Oct 2023 13:48:47 +0200, Jan Brothánek wrote:
> Hi,

> I ran into a bug occasionally causing output frames with gray stripes (see
> screenshot and output.mp4 in links below), using slices. Reproducible with
> these parameters (originally found using API) and input.mp4 (link below):

> x264 --bitrate 8000 --vbv-bufsize 1600 --vbv-maxrate 8000 --output-depth 10
> --profile high422 --output-csp i422 --preset ultrafast --tune zerolatency
> --threads 16 --slices 16 -I 120 -b 0 -o output.mp4 input.mp4

> Tested with 5a9dfdd (latest master), 5db6aa6 (from Ubuntu repo), aaa9aa8
> (from Centos7 repo), and 90a61ec. The bug seems to be non-deterministic but
> demonstrates similarly on similar frames - a complex scene followed by a
> simple scene that fades to white or black. It looks like the probability of
> corruption increases with the number of threads (that's why I used 16) and
> the VBV size limitation.

> screenshot of input frame:
> https://drive.google.com/file/d/1ZiVU5BrKYY_pWr-VzstnOl3AbcW96PhE/view?usp=drive_link
> screenshot of output frame:
> https://drive.google.com/file/d/1MhxC8GaKOfnCL11nPt2jsTVbX6kigVq_/view?usp=drive_link

> input.mp4:
> https://drive.google.com/file/d/1e8abTsbs8R-CxNNLDKy1jAfR66-guQMt/view?usp=drive_link
> output.mp4:
> https://drive.google.com/file/d/1YzcjVGkmzsHvGTXiOh1rVCXGTKw5kIVW/view?usp=drive_link

> Best,
> Jan

Hi.

Quick fix:
https://code.videolan.org/BugMaster/x264/-/commit/324317619c109345759116aba06debb4d00b4c36

I'm not sure that this is a completely correct patch and that it won't
cause VBV overflow, but in your case it should work. So if you have
other streams with a similar problem, you can check it on them. And
check that VBV overflow does not occur anywhere.