I sometimes need to encode video recorded with my Canon A430 digital camera to a format that works, so I want to convert it to xvid. The sound stream included is so weird (PCM at 11024 Hz, no, not 11025 Hz) that encoding with sound always results in async video/audio. Therefore I don’t encode sound. I use this: 

mencoder video.avi -o video.xvid.avi -ffourcc XVID -ovc lavc -lavcopts vcodec=libxvid:mbd=2:v4mv:vqscale=4:aspect=4/3 -nosound

The vqscale can be made 3 for slightly higher quality, but with the crap quality it starts with, there is not much use.