[FFmpeg-devel] [PATCH] webp: fix transforms after a palette with pixel packing.

[Maryla Ustarroz]

We've just added a file to libwebp-test-data that covers this case:
https://chromium.googlesource.com/webm/libwebp-test-data/+/refs/heads/main/dual_transform.webp
FFmpeg currently fails to decode it, but it works with this patch.

My understanding is that an ffmpeg developer needs to upload the file to
fate, and then I can add a fate test to the patch?



On Fri, Aug 20, 2021 at 7:07 PM James Zern <jzern-at-google.com at ffmpeg.org>
wrote:

> On Thu, Aug 19, 2021 at 12:56 AM Maryla <maryla-at-google.com at ffmpeg.org>
> wrote:
> >
> > When a color indexing transform with 16 or fewer colors is used,
> > WebP uses "pixel packing", i.e. storing several pixels in one byte,
> > which virtually reduces the width of the image (see WebPContext's
> > reduced_width field). This reduced_width should always be used when
> > reading and applying subsequent transforms.
> >
> > Fixes: 9368
>
> Is there anything in
> https://chromium.googlesource.com/webm/libwebp-test-data that covers
> this or can you add the file from the ticket to fate?
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