Mencoder

Hint: all video filters (-vf option) can be previewed using mplayer before starting the actual encoding procedure.

DV to MPEG4 with deinterlacing

Encode a raw DV file from a digital video camera to MPEG4 video with mp3 audio.

mencoder input.dv -vf pp=lb -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=2000 -oac mp3lame -lameopts vbr=3 -o output.avi

Adjust vbitrate to your needs. vbitrate=2000 produces a quite good quality at a small filesize for videos in TV standard resolution.

Scaling and MPEG4 encoding

Scale a high resolution video down to a lower resolution, preserving the aspect ratio. MPEG4 encoding options as usual. This scales any video that mencoder is able to read to a 480p video (480 pixels high).

mencoder input.mov -vf scale=-3:480 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=3000 -oac mp3lame -lameopts vbr=3 -o output.avi

-vf scale=-3: calculates the with of the video using the original aspect ratio and the desired height.
Other scaling options as noted in mplayer´s manpage:

 0:   scaled d_width/d_height
-1:   original width/height
-2:   Calculate w/h using the other dimension and the prescaled aspect ratio.
-3:   Calculate w/h using the other dimension and the original aspect ratio.
-(n+8): Like -n above, but rounding the dimension to the closest multiple of 16.