[FFmpeg-devel] [PATCH] WebP native muxer bugfix: frames should have alpha blending off

Michael Niedermayer michaelni at gmx.at
Thu May 28 02:32:45 CEST 2015

On Wed, May 27, 2015 at 03:10:05PM -0700, Urvang Joshi wrote:
> All the frames that the native muxer gets are fully reconstructed
> frames,


>  and they should not be alpha-blended with the previous frames.
> As per the WebP container spec
> https://developers.google.com/speed/webp/docs/riff_container#animation,
> ANMF chunk should specify blending method = do not blend (and disposal
> method = do not dispose).
> However, the native muxer was wrongly setting blending method = use
> alpha blending.
> This bug can be reproduced by converting a source with transparency
> (e.g. animated GIF with transparency) to an animated WebP, and viewing
> it with vwebp.
> ---
>  libavformat/webpenc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

this breaks the encoder completely
the testcase is the same as previously but probably any testcase that
enables encoding multi frame animations will do
try  -cr_threshold 10000 -cr_size 16 for example

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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