Actually instead of messing around with my pc's codec situation, i decided to try wiping out my PMS installation completely (the folder in Program Files + programdata PMS.conf files + Mplayer stuff in %appdata%) and reinstalling SB66 in it's "vanilla" form. Now those MKVs are working fine! And I can play them using either TSMuxer or Mencoder, both are working perfectly. No framerate skipping and perfectly-synched audio.
This means there was something in my old configuration which was causing this! I'm presently going to try changing each setting one by one and see if I can isolate the setting which caused the issue.
EDIT: Found the culprit. It happens if "A/V Sync Alternative Method" is turned OFF. That setting is turned ON by default in a vanilla installation, and in that case the sync + framerate smoothness is perfectly fine. What I don't understand is why that setting will affect tsmuxer behaviour! Since it's in the MEncoder section.
Last edited by Coltaine79
on Fri Mar 02, 2012 6:54 am, edited 1 time in total.