High speed playback 8x, 16x, 32x

[luke at 3degreemedia.com (Luke Massey)]

I am using a named pipe to control mplayer and can't get it to play back
above 4x.  The man page says up to 100x should work, but when I try to
set playback speed above 4x, Mplayer just sets it at 4x.  I was
wondering if this might be a limitation of the video codec or the remote
control protocol.  I can re-encode the video in any format necessary.  I
also don't mind modifying source code if I need to.  What can I do to
get MPlayer to play back at 8x, 16x, 32x, etc.?