Thanks so much for your help!
Sorry that I didn’t yet come across the all-important info about H.264. I’m new to video but an old pro audio engineer.
I don’t see an option in MPEG Streamclip to export to ProRes or ProRes LT. In fact, I had never heard of that before your advice. When selecting export to Quicktime, it DOES NOT show under the compressor dropdown. I have poked around some more and read some of the other posts here. I am running an older version of FCP (5 I believe) so perhaps it did not come with that 422 codec? Not sure. Anyway, I need another option to convert my file to as I now understand Apple did not accommodate for cutting mp4 or H.264. Any other suggestion would be welcome.
Best,
Todd