Hi Jim,
This did not work for me, my Blu-ray reacted with 'corrupt or unsupported file' I tried many combinations, but in the end had to admit defeat.
In desperation I tried a programme called handbrake and ran the original MPEG4 H.264 AAC file through that, keeping all the video settings the same and just altered the audio codec there to AAC(ffmpeg) as I could not see a AAC LC(MUSIC) and this option seems to have cured my problem. I need to test a bit more to see what, if any, difference there are between the iMovie version and the one edited in Pr and altered in Handbrake.
I wonder why Pr does not include the LC codec?
Thanks again for your time and your swift replies.
Best regards
Doug