It looks like by default the first frame is the thumbnail seen in Mac Finder/Windows Explorer. I have an animated intro that starts out completely white though, so I want to set the thumbnail to the 8 second mark. Is there a way to do this in Camtasia Studio for PC?
We were just exploring this for another user today! Unfortunately, at least on Windows, I haven't been able to find a way to do this. I'm running Windows 8.1 and I think I've exhausted the options for an .mp4 that's viewed in Windows Explorer. It's funny that you say it seems to be using the first frame, though. On my system, it seems to be using a frame from about 4 seconds in.
I'm less familiar with Mac Finder, so I can't give a definitive answer there.
Also, I'm sure you found options for setting the thumbnail image when hosting your video on screencast.com, YouTube, etc. But you're right in that the file thumbnail itself seems to be at the mercy of the operating system.
I wonder if anyone else has found a solution. If so, maybe they'll post.
Thanks for using Camtasia. Sorry I didn't have a better answer.