me@there ~/Videos $ ffmpeg -i compiz.asf compiz.gif
ffmpeg version 0.8.1-4:0.8.1-0ubuntu1, Copyright (c) 2000-2011 the Libav developers
  built on Mar 22 2012 05:29:10 with gcc 4.6.3
This program is not developed anymore and is only provided for compatibility. Use avconv instead (see Changelog for the list of incompatible changes).
Input #0, asf, from 'compiz.asf':
  Duration: 00:00:33.27, start: 0.000000, bitrate: 528 kb/s
    Stream #0.0: Video: wmv2, yuv420p, 1360x764, PAR 64917:65024 DAR 403904:227273, 1k tbr, 1k tbn, 1k tbc
File 'compiz.gif' already exists. Overwrite ? [y/N] y
[buffer @ 0x9620ca0] w:1360 h:764 pixfmt:yuv420p
[gif @ 0x961fde0] ERROR: gif only handles the rgb24 pixel format. Use -pix_fmt rgb24.
Output #0, gif, to 'compiz.gif':
  Metadata:
    encoder         : Lavf53.21.0
    Stream #0.0: Video: rawvideo, yuv420p, 1360x764 [PAR 64917:65024 DAR 403904:227273], q=2-31, 200 kb/s, 90k tbn, 1k tbc
Stream mapping:
  Stream #0.0 -> #0.0
Could not write header for output file #0 (incorrect codec parameters ?)