[MEncoder-users] Extracting every 10th frame

[DaveG]

Is there an obvious/easy way to extract every 10th frame from a video file?  
Or every 20th etc.

The only obvious method I can see ATM is

mplayer source.mpg  -benchmark -nosound -vo png:z=0

followed by deleting all frames/files where the name doesn't end in 0.png and 
then re-encoding the remaining 10% of frames resulting in a video which plays 
back at 10x original speed.

Source video is MPeG-PS
-- 
Dave