[MEncoder-users] framerate control question

[pfile at pacbell.net]

lets say i have a video which was encoded at 60000/1001, with 10,000  
frames. through decimation of 3 frames out of every 5, i now have a  
video with 4,000 frames intended to be played back at 24000/1001. in  
theory, these two movies should have the same playback time.

in this situation, why does mencoder have to insert duplicate frames  
to maintain the proper framerate? are the extra frames required  
solely due to rounding error in the frame display time? i've observed  
that with -noskip -noencodedups, the video is always about 6% shorter  
than it is supposed to be.

i'm wondering how in heck to get a nice smooth 24p version of a 60p  
ATSC transmission which doesnt require timestretching the audio.

thanks,

rob