[artam]

BS Player (testing on 2.43) has serious shortcomings when playing MKVs and it's sometimes really annoying to play MKVs as they are not played as they were intended to play by container creator. :-(

The MKV container allows two flags for the tracks - "default track flag" and "forced track flag" - and I think that the good player must allow to play the streams according described flags in the container.

It means that in the case of MKV with for example 5 audio tracks if you have the 1st, 2nd, 3rd and 5th tracks flagged as default=NO and the 4th is flagged as default=YES, the player must play the 4th track as default. The same apply for subtitle tracks as well.
BS Player doesn't do that (at least I didn't found the way), still plays the 1st tracks as default. So there is still lot of work on BSPlayer. ;-) For example, Media Player Classic does this correctly, mhmm... :-|