Since it sounds like you want a pretty hefty speed-up (not just 1.5x or 2x) it's probably best to do something that will actually drop the frames, such as mencoder, which would look something like:

Code:
mencoder -nosound -ovc lavc -lavcopts vcodec=mpeg4:vqscale=3
-vf framestep=30 -fps 900 -ofps 30 -o outfile.avi infile.avi


Assuming the input was at 30 fps and you want a 30x speedup. It requires re-encoding, which will degrade the quality a bit, but sometimes it can be tough to playback a 30fps video at 900fps. Adjust the framestep, fps, and ofps to match the parameters for your source video.
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- Tony C
my empeg stuff