[FFmpeg-devel] [PATCH 1/2] libavcodec: add support for animated WebP decoding

[Lynne]

Jul 8, 2020, 06:28 by josef at pex.com:

> Fixes: 4907
>
> Adds support for decoding of animated WebP.
>
> The WebP parser now splits the input stream into packets containing one frame.
>
> 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.
>

We don't convert pixel formats in decoders, and I wouldn't want to have libavcodec
depend on libswscale. I wouldn't trust libswscale to make accurate conversions either.

Can you use the macros in libavutil/colorspace.h to convert the BGRA value to YUVA
and then just memcpy it across the frame?

Also, there are a lot of frame memcpys in the code. Could you get rid of most of them
by refcounting?


> -    .capabilities   = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS,> +    .capabilities   = AV_CODEC_CAP_DR1,
Why?


> +            if (component == 1 || component == 2) {> +                height = AV_CEIL_RSHIFT(height, desc->log2_chroma_h);> +            }
We don't wrap 1-line if statements in brackets.