Every quicktime movie trailer at apple.com crashes mplayerplug-in version 3.45.
To demonstrate, go to http://www.apple.com/trailers/independent/goyasghosts/
Play the "Trailer".
WMV, DIVX, and Real media play without issues.
I just reproduced this issue by downloading the source tar.gz and reinstalling.
The previous version that I had (3.31), packaged as Ubuntu "mozilla-mplayer" didn't crash but had very grainy video compared to downloading and playing it in the mplayer command line which was quite clear.
Audio has never been an issue.
I have the latest w32codecs installed.