[Brent Wagner]

I believe I have a solution. I had this issue too and I lost days of editing time troubleshooting. 99% of the data out there suggests an issue with the quicktime video plugins, but after trying to replace them and/or clear out any caches with reboots, re-installs, different OSes and Vegas versions, I finally stumbled upon the solution.

I noticed the same problematic MOV files worked in a new project, but I didn’t want to start all over. I suspected my project file, so I opened a second instance of Vegas in a new window, then I used Ctrl+A to select everything on the timeline and I copied it to the new window. However, this triggered the issue in the new, Untitled project as well!

When pasting the full contents of my broken project, I noticed the last couple of clips had green thumbnails in the new window, indicating some kind of video corruption. I started another new project and this time I copied everything except those last few clips (Ctrl+A then Ctrl+left click to de-select) and worked!!

I hope this solution works for you too. In hindsight I should have suspected the clips I had added just prior to hitting this problem, but it was so widespread (even MOV files from File Explorer opened in the trimmer would go dark after a few frames) that I didn’t think of it until after I discovered the solution.

Good luck!