[FFmpeg-devel] [PATCH] fix for transparencies in animated gifs

[Bjorn Roche]

Sorry for the very delayed response, Carl:

On Tue, Nov 21, 2017 at 6:55 PM, Carl Eugen Hoyos <ceffmpeg at gmail.com>
wrote:

> 2017-11-21 18:53 GMT+01:00 Bjorn Roche <bjorn at giphy.com>:
> > Support for transparencies in animated gifs requires modifying both
> > libavcodec/gif.c and libavformat/gif.c because both the graphics
> > control extension (handled by libavformat/gif.c) and the raw frame data
> > (handled by libavcodec/gif.c) must be changed.
>
> Does remuxing animated gif with transparency work with your patch?
>

A command like this:

    ffmpeg -i in.gif out.gif

seems to produce the same output as before: transparency replaces with
opacity. However a command like this:

    ffmpeg -i in.gif  -vf palettegen -y /tmp/pal.png && ffmpeg -i in.gif
-i /tmp/pal.png -lavfi paletteuse -y -f gif out.gif


produces an output that looks like the input (including transparency).


I believe this is a problem with the decoder, however, since


    ffmpeg -i /Users/bjorn/Desktop/smoketrail.gif
/Users/bjorn/Desktop/smoketrail-out%d.png


produces opaque images as well.

-- 


Bjorn Roche

Sr. Video Pipeline Engineer

bjorn at giphy.com