[FFmpeg-devel] [PATCH] avcodec[/format]/webpenc: use WebPAnimEncoder API to generate animated WebP

Urvang Joshi urvang at google.com
Fri Apr 17 00:40:14 CEST 2015

On Thu, Apr 16, 2015 at 3:09 PM James Almer <jamrial at gmail.com> wrote:

> On 16/04/15 4:18 PM, Urvang Joshi wrote:
> > Hi,
> > Here's the patch without whitespace changes.
> >
> > Thanks,
> > Urvang
> This patch doesn't apply cleanly. Looks like something weird with the
> indentation still.
> Was this patch handmade? It says the hash for libwebpenc.c is 95d56ac
> (same as git head),
> but the contents of the patch don't match.

Sorry, I should have mentioned that it was created with
"--ignore-all-space" option, so using the same option when applying the
patch would have worked.

But to avoid any confusion, here's the re-created patch, that should apply
cleanly with just 'git am'.

> After fixing the conflicts and compiling the patch seems to work, but the
> resulting
> animated webp files are smaller than those using the native muxer using
> the default
> encoding and muxing settings.
> Is this because the muxing done by libwebpmux is different, or are the
> quality defaults
> changed in any way when using this codepath? If the former then that's
> pretty good, but
> if the latter then it should probably be fixed.

Short answer: muxing done by libwebpmux is different, so it's expected that
it generates smaller WebP files.

Detailed answer:
The native muxer is naive, and it always uses X offset and Y offset of 0
for all frames. This means the full width x height of all frames are
libwebpmux muxer is smart on the other hand: for example, it only encodes
the part of the frame which has changed from previous frame.
This and other optimizations result in smaller WebP files.


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