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

[Carl Eugen Hoyos]

2017-11-27 18:50 GMT+01:00 Bjorn Roche <bjorn at giphy.com>:
> 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.

remuxing == -vcodec copy

What about ffmpeg -i in.gif -vcodec copy out.gif ?

> 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

This produces transparent images here for the output
file of ticket #6813.

Carl Eugen