Thanks for the suggestion! I tried it out, but I can't seem to get it to run. It appears to freeze upon opening it. It's doing something according to Task Manager, but upon checking Bitdefender's whitelist (it initially blocked it), it says it's apparently "never been run" (paraphrasing).
I have the codec installed. Edit: Upon attempting to test it, none of these opened or played, but I could open the files and play the videos manually ... Hmm.
Now I'm really upset because this seems like great software with a lot of options. I tried changing the CPU in the codec manager settings (I have no problem running the associated codec file), changing what graphics card the file opens with, but no luck. Running it as an Admin, or in compatibility mode doesn't seem to help either. The most frustrating thing is that there isn't even a clear problem. Augh!
Edit: If I try to open it in safe mode, the error message "GetDefaultAudioEndpoint" shows up, but not when attempting to open it normally. : /