[vlc] Good diagnostic tools for MKV and MP4

[PK]

I've recently run into several problematic MKV and MP4 videos, one of which 
brings up an evident bug in vlc.  (I've filed a ticket.)  Perhaps these 
videos have structure problems, and I'd like to diagnose them.

Can you recommend software to diagnose -- and if possible, repair -- 
structure problems in MKV and MP4 videos?  I'm most interested in H264 
streams, and the platform for now is Windows XP.

Thanks.

djc