[MEncoder-users] 720p 50fps, encode to 25fps, -ofps doesn't work properly

[Michael Holland]

Folks,
I'm wanting to compress a 720p DVB broadcast (from ABC Australia).
The source if high-def 25fps video, so each frame is shown twice
in the 720p 50fps broadcast.
    I want to encode as 25fps, so I tried '-ofps 25', but the result
is awful. Single-stepping in mplayer shows there are still lots of 
duplicate frames, and so lots of skipped frames also, from original 
25fps source.
    How can I tell mencoder to just take every second frame from the
50 fps input?

Am using:
$ mencoder -oac mp3lame -lameopts preset=160 -ovc lavc
    -lavcopts vcodec=mpeg4:vhq:vbitrate=4000  -ofps 25
    <filename>.ts -o <filename>.avi -sb <start> -endpos <seconds>

I've uploaded a few seconds of input MPEG to 
ftp://ftp.mplayerhq.hu/MPlayer/incoming/PE-DVB-720p-a.mpeg
(where does that go to?)

Mencoder version is SVN form 5th July.