[FFmpeg-devel] [PATCH v1 3/4] libavcodec/webp: add support for animated WebP decoding

[James Zern]

On Thu, Jun 8, 2023 at 7:21 AM Thilo Borgmann <thilo.borgmann at mail.de> wrote:
>
> From: Josef Zlomek <josef at pex.com>
>
> Fixes: 4907
>
> Adds support for decoding of animated WebP.
>
> The WebP decoder adds the animation related features according to the specs:
> https://developers.google.com/speed/webp/docs/riff_container#animation
> The frames of the animation may be smaller than the image canvas.
> Therefore, the frame is decoded to a temporary frame,
> then it is blended into the canvas, the canvas is copied to the output frame,
> and finally the frame is disposed from the canvas.
>
> The output to AV_PIX_FMT_YUVA420P/AV_PIX_FMT_YUV420P is still supported.
> The background color is specified only as BGRA in the WebP file
> so it is converted to YUVA if YUV formats are output.
>
> Signed-off-by: Josef Zlomek <josef at pex.com>
> ---
>  Changelog               |   1 +
>  libavcodec/codec_desc.c |   3 +-
>  libavcodec/version.h    |   2 +-
>  libavcodec/webp.c       | 714 ++++++++++++++++++++++++++++++++++++----
>  4 files changed, 658 insertions(+), 62 deletions(-)
>
> [...]
> +
> +            bytestream2_skip(&gb, 2); // loop count is ignored

TODO? APNG and GIF support looping and have -ignore_loop to control it.