Jim, lately I've gotten complaints on YouTube using an out of the box (whoops...no box anymore!) YouTube export through AME. It wants the Moov Atom at the top; AME makes it but places it at the end of the file where YT can't see it until it's finished uploading. I sort of thought one of the reasons for the YT formats to be 2-pass is so that the metadata in this file can be created and correctly placed after the first pass.
There is at least one free, simple app that will fix the files called MP4 Fast Start; I wish I didn't have to run files created in the (rather expensive) Adobe suite through some free gadget before I can upload them...Original footage is XAVC-S from an FDR-AX100 camcorder massively edited and processed out as a 1080p MP4.
Getting slightly off-topic but maybe not, as the complexity may affect the YouTube uploads: I'm doing one-camera shoots of operas, leaving the camera wider than usual and editing my shoot in Premiere as multi-camera. This means I can add cuts and dissolves to the usual menu of pans and zooms (which can now also be added using the Motion effects in PPro). A typical result: "Un bel di" from MADAMA BUTTERFLY, which also has a link to a "reference copy" that is an unedited camera image: Sara Beth Pearson sings "Un bel di" from MADAMA BUTTERFLY - YouTube. Enjoy! Love to get some feedback on this as I think it's a relatively unique process to the capabilities of that camcorder.