I stumbled over the exact same problem described in the original post a few days ago. In cooperation with the techsmith support I found out that Camtasia obviously has problems with very big video source files, which is of course inconvenient, but avoidable if known.
I had a 40G video source file, of which I used only a part in seperate smaller projects. Behaviour as described above. Then I tried it with <4G video source files, adding them up in the timeline, and the rendering at least started, though I didn't take the time to let it finish, since my projects are 90 mins each and I need to recut first.
All in all, I really think this was the problem, even if the original big file was handled, cut and treated perfectly in the timeline view. The rendering routine however seems to need smaller source files. The techsmith guy said something about <10G, but I tested with <4G and since this is a comprehensible 32bit barrier, I think you should be save with that.
Best Regards and good luck!
There have been some changes to the rendering over the past year, so the new issue might not be the exact same as the original post. Please open new support tickets for personnel to look at your project specifically.
Thanks and regards,
We want to thank you for your patience while we worked to improve Camtasia. Camtasia 9 is a 64 bit application and that has substantially helped us to improve performance, stability, the ability to work with more complex projects, allows Camtasia to take advantage of more resources if you have a more powerful machine, and allows Camtasia to edit and produce larger video dimensions. Most of these benefits will still only be noticeable on stronger machines (see our system requirements). Video editing and rendering is a very computationally intensive process unfortunately.
We have found having access to more computer resources has resolved many of the issues we saw in version 8.x, especially when working with large video files. If you're running 64-bit Windows, you can download the free trial here.
Please feel free to post your feedback and feature requests here in our Community forums and remember, all technical support-related inquiries should be directed to our dedicated Technical Support team at https://support.techsmith.com/
Apologies for the inconvenience and the wait,
Senior Software Engineer, Camtasia Windows