[FFmpeg-devel] [PATCH] svq1dec: Ensure that pixel format constraints are respected

[Vittorio Giovara]

2018-07-17 21:39 GMT+02:00, Carl Eugen Hoyos <ceffmpeg at gmail.com>:
> 2018-07-17 21:39 GMT+02:00, Vittorio Giovara <vittorio.giovara at gmail.com>:
> > YUV410P requires that sizes are divisible by 4. There seem to be
> > some encoders that ignore that and encode a different value in
> > the bitstream itself. Handle that case by exporting the relative
> > cropping information.
>
>Can you provide a sample?
>
>Thank you, Carl Eugen

It is possible to generate samples affected by this bug with the svq1 or
ffv1 encoders, like this:

./ffmpeg -f lavfi -i testsrc -s 190x240 -t 1 -pix_fmt yuv410p -c:v ffv1 output-yuv410p.avi

A prime example where the generated sample will fail is with a strict
scaler, such as zimg:

./ffmpeg -i output-yuv410p.avi -vf zscale -f null -

which will fail with

code 1027: image dimensions must be divisible by subsampling factor
Error while filtering: Generic error in an external library
Failed to inject frame into filter network: Generic error in an external library
Error while processing the decoded data for stream #0:0


While the proposed patch won't directly fix the issue with zscale, it will
offer tools for API users to adjust sizes accrodingly, and avoid it
altoether.

Regards,
    Vittorio