No Video Playback (Black Video window and thumbs)

Hi,



I can't make Pro Tools 12 to play any Video file. When i import a video (or open a session with video in it) video thumbs and video playback window are black, when i start playback it stays black and Pro Tools throws an error after i stop.

What i have tried so far:

- Change Playback Engine, disable re-enable Video Engine (Avid Video Engine shows up in activity monitor and stays there, seems to initialize and run fine)

- Trash Preferences

- Set up a new partition for testing, installed clean OS X 10.10, then 10.9., installed clean PT 12, then 11, Results are always the same, regardless which combination i choose (after each try i completely trashed the partition and started over)

- Installed Avid Codecs LE



I can play back the video files in OS X without problems (.mov, DVC and h264).

I installed PT 10 for testing and it just works fine with the same files.

I'm quite clueless right now what else to do so i hope somebody has some suggestions.



Thanks!