Whenever i use Finder to go to a folder with an MKV file in it, the QTKitServer Process starts up hogging the CPU with 50-100%. As long as the folder is open this doesn't change. Even after i close Finder or navigate to another folder the CPU usage remains high for about a minute or two. This is especially a problem when I'm on battery power. The estimated time remaining goes down to about 3 hours on my rMBP. I have found out that this process is in charge of creating the thumbnails that are displayed in Finder. It just seems to choke on (some?) MKV files. At first i tried "CMD+J" to uncheck "show icon preview". Unfortunately this didn't do anything. A Google search led me to this thread, where a corrupted avi file created the same issue. There it is suggested to delete the video file that is causing the problem. In my case this is not an option because the file isn't corrupt and works perfectly in VLC. As a quick fix i renamed the "Movie.qlgenerator" file in the /System/Library/QuickLook/ folder. This, however, disables thumbnail creation for all movie files, not just MKVs! Is there any way to configure the creation of thumbnails in Mountain Lion to just exclude MKV files? Or maybe exclude a folder?