One silly trick:
Just rename the file.
Really.
Just rename it from .M4V to .MP4
It's possible that your application just doesn't recognize the .M4V extension.
Old thread but just signed uo to say thank you, not only did it work but it solved 2 problems, the 2nd being an audio sync delay. Simply renaming from m4v to mp4 put the audio back in sync and the file extension is recognized and plays perfectly. Who would thought, thanks again.