Here’s a simple start for you:-
1] Track1 has the Video you wish to have within your Letter/s
2] Make a Track2 (T2) a “Child” of Track 1
3] Set T1 to “Multiple Mask” in its Track Header
4] Add a Media Generator Text Event to T2
Job Done!
Now, this WILL have your Video within the boundaries of your text, against a Black BG. If you wish, place “another” Video Event on a new video Track, T3. This will now become your Video BG for your Text-IN-Video Letters.
There’s much creativity to be had messing with the Track Header and its Compositing Modes – be warned!! It’s thoroughly addictive…..
Grazie