The project the thread starter mentions makes a certain library / extension mandatory on the server that hardly exists on webhosted servers. Coppermine's target audience are people on "regular" webhosting, so this will not go into coppermine's core code. We'd love to see a contribution (preferably as a plugin) that makes this an optional component, but (as I said) it will not go into the core.
The project the original thread starter refered to does not add the capability to coppermine to create thumbnails from videos, the necessary code in coppermine hasn't been created yet. It's only a theoretic hack that could be accomplished if anyone was ready to look into this. The dev team won't, so this goes unsupported anyway.