Ah, thank you. I didn’t know that about MP4s/MP3s. I am currently using the free version of DaVinci.
When I go back and look at the codec information, the file that did work lists the codecs as “Timecode, MPEG-4 AAC, H.264”
When I look at some of the other videos that did not upload, some list the codecs as “MPEG-4 AAC, H.264”. The other files are MP3s and don’t give me any of that information in a place I can find easily (I’m on Mac).