Muxing with MEncoder: lost frames

[ar]

I've just tried this:
$ mencoder -ovc copy input.mpg -of mpeg -mpegopts format=mpeg2:vwidth=720:vheight=576:vaspect=4/3:vframerate=25 -o output.mpg
DGDecode says that there are 6500 frames in input.mpg, but output.mpg consists of only 6499 frames (one prefinal frame was lost due to transmuxing).
Can someone explain this to me?
Thanks in adance.

[Tack]

Could be that mencoder dropped a frame for a/v sync reasons. Try -mc 0 and see if that helps?

[Midzuki]

BTW, the "missing-frame issue" was not uncommon when I (re)muxed various MKVs, or encoded VC-1 into an ASF container instead of an AVI / elementary stream... :confused: