Yes, I thought of this method, it hasn't worked for me for a while either.
This method turns an image texture into a video texture with a little trick.
It doesn't always work that way for me.
What works ( and you also tried this), is to put video material on the surface and replace it. But I guess you didn't replace it, but wanted to choose a new one (your own) and it didn't work.
I think you should try to simply replace it first.
So drag the original video you find in the library onto the surface and just open another one.
If you click on the texture (which is a video here), the menu will appear. Here you can open your own video from anywhere on the hard drive with the "open" button and don't have to trick with the file format.
You don't need to copy your clip to the TM library, just find it where it is.
I'm curious if it works that way for you or not.....
