Before someone points me toward the FAQ: I've already tried the method described therein. All the remuxing in the world does not get most of my MKVs to play. With "don't play" I mean: The Sony Bravia let's me select the file, I see a "Dolby Digital" popping up and that's about it. Black screen, no sound.
I even took the settings from the MKV that do play and tried to copy those on the ones that don't.
No dice. The debug.log does not show any error or any information indicative of a problem.
As a kind of last resort, I've tried transcoding using Handbrake (only the first minutes of one particular MKV, mind).
No dice, either.
Which means I'm fresh out of ideas where to look next. Could someone point me in the right direction? I might add that another DLNA-Server (Mezzmo, which also uses ffmpeg) seems to have a related problem (though in that case I'm getting sound and a corrupted first frame with the same MKVs).