When I use mplayer to play DVDs that have high bit rate scenes I find that one of two things can happen:

a. Sound starts to be clipped and sounds "electronic".

or

b. Frame rate slows down to stop while sound continues to play, when the decoder reaches lower bit rate video the decoded frames are pushed out of the buffer at faster than normal speed until sound and video are synced again.

This only happens with a few of my DVDs and only once per DVD. I set an 8MB cache in the options. I tried pausing the movie in the hope that this will let the decoder catch up, but it doesn't work. I shall have to investigate -framedrop.