Yep, Rockbox works with it:
Gigabeat F series:
As of April 2007, Rockbox now includes video-support for MPEG playback through the included work-in-progress mpegplayer plugin. [2] The mpegplayer plugin supports MPEG-1 and MPEG-2 video streams with MPEG audio (layer II/III) multiplexed into .mpg files with no hard limits on frame rate or bitrate. Files must be encoded at native screen resolution. Seeking is not yet implemented.