[FFmpeg-devel] FAQ item on GIF demux

François Revol revol
Fri Nov 2 23:12:20 CET 2007

I tried to convert an animated GIF file today, but the result was quite bad.
Checking the file with identify (ImageMagick) gave something like:
ALCHIMIE7_89.GIF[0] GIF 164x104 164x104+0+0 PseudoClass 256c 1mb 20358.035u 1:08
ALCHIMIE7_89.GIF[1] GIF 160x16 164x104+2+86 PseudoClass 256c 1mb 20355.665u 1:08
ALCHIMIE7_89.GIF[2] GIF 160x100 164x104+2+2 PseudoClass 256c 1mb 20355.151u 1:08
ALCHIMIE7_89.GIF[3] GIF 158x84 164x104+4+2 PseudoClass 256c 1mb 20352.767u 1:08
ALCHIMIE7_89.GIF[4] GIF 155x83 164x104+7+2 PseudoClass 256c 1mb 20350.854u 1:08
ALCHIMIE7_89.GIF[5] GIF 157x90 164x104+4+2 PseudoClass 256c 1mb 20348.928u 1:08
It turned out the file used delta-like images which ffmpeg doesn't handle.
It seems ImageMagick itself has difficulties processing this kind of files 
Google came out with a nice workaround:
Using convert -coalesce merges the deltas to each image (=makes them all 

It could be a nice addition to the FAQ:
"I tried to convert a GIF animation, the first frame looks good but next 
ones look inverted or distorted."

Could also fix the demuxer but it's probably not worth the pain.


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