x265 Encoding Issue with MP4Box

[sbilodeau]

-> try disabling '--repeat-headers'  (x265->Misc->Random Stuff->Repeat headers)

This fixed the blacked out first GOP in the MP4Box mux. Still not sure why the FFMPEG one still fails, but at least I'm able to get usable files - I'll submit a bug report to MP4Box dev group to see if they can fix what's causing it!

Thanks for your help!