Dozens of M4V files suddenly unplayable in QuickTime

At some point in the last few weeks, many of my M4V files have become unplayable. I have about 200 or so such files that are ripped from my DVD library using HandBrake (various versions over the years) and I play them both on iPads and Apple TVs. They are stored on a NAS and served via iTunes from an older Mac mini. The devices are all iOS 7 and the Apple TVs I just upgraded to gen 3 models.

When playing via iTunes, I get the message, "This movie requires QuickTime, which is not supported by this version of iTunes."

When opening them directly in QuickTime player, the message is "QuickTime Player can't open "<filename>.m4v".

Most discussions about this subject are around iTunes and re-adding the files to the library or using the 32-bit version. However, I have ruled all this out by pulling an affected file over to my MBP and attemping to open it direct.y in QuickTime. This does not work.

Things that have changed recently that I don't think are related but might be helpful:

• Ran iFlicks against the whole library to correct metadata and artwork (awesome!)
• Removed an Apple TV 2 and added 2 Apple TV 3's
• Attemped to update Plex media server to the latest version and got shut out because my Mac mini doesn't support 64-bit code.

I can't imagine the latter has anything to do with it but, who knows. I am not using Plex to serve any of this stuff.

Some files are OK and some are not. I cannot find any commonality between the misbehaving files.

Any ideas here?