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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.
 
iSkysoft iMedia Converter

iSkysoft iMedia Converter converts Apples files to regular mp4.

doing it now, works great.
 
I think there is an app produced by noteburner that converts DRM m4v files. You can try it out for the first minute of the video, but from memory the full version of the app costs $50. Which is a lot for something that might stop working if Apple decided to do something about it.
 
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