iTunes video playback is scrambled since update to iTunes 12.7.3

I had the same issues, and had Apple engineers go through my iMac with no luck. I eventually solved it myself by doing a full reload of the OS from App Store -> macOS High Sierra -> download. The original download was a partial, updating from 10.13.2 to 10.13.3 and resulted in garbled video (audio fine) in both iTunes and QuickTime Player. My sense is that iTunes and QTP could not decode .m4v files, but .mp4 files played with no issues. I reloaded iTunes, but with no luck, getting the following when playing a .m4v movie...

After full download (4.8GB - sigh) and re-installation of the OS, everything worked fine in both iTunes and QTP. Perhaps there was an issue with the incremental update that the full download was able to rectify. I can't guarantee this will work for everyone (I know of someone else with the same issue on another thread/question that did this with no luck), but it worked for me. I was watching a video in iTunes when I received notification of your post...

Thanks to DadToTheBear for the help with my iTunes video problem. Had to reinstall the

MacOS using the recovery partition and the following article: How to reinstall macOS - Apple Support. After reinstall, all seems to be fine with iTunes video on my iMac.

It sounds like you can still play .mp4 videos? iTunes videos are .m4v, which are basically .mp4 with DRM-encryption. In my case (same issue, same iMac, same OS and iTunes versions as you) I think the updated iTunes and QuickTimePlayer are unable to decrypt iTunes videos, as both can still play .mp4 videos correctly. It sounds like you have the same issue?

Same problems after update on my iMac. Tried safe mode and resetting NVRAM. No luck.

Any video downloaded from iTunes store plays back pixelated/garbled. Audio fine. iTunes

purchased videos downloaded to my iPad or iPhone via iMac iTunes seem to be fine so file

integrity seems to be OK. Playback of any non-DRM files on my iMac work fine.

Anyone else have success?

I have the same issue - video scrambled, audio fine - also the very same iMac, same OS, same version of iTunes (12.7.3.46).

I rebooted, reloaded iTunes, to no effect. I can play DVDs through a linked DVD player, and can also play trailers from the iTunes Store, but no downloaded movie or TV show from iTunes will play with unscrambled video.

OK, thanks for the update/tip. I was hoping to avoid having to do a complete reload/restore of my system but I guess that's the only alternative at this point. I think you are correct that the incremental update on my iMac messed things up. I tried downloading the older 12.6.3 version of iTunes and it displayed the same behavior.

This method worked for me too. Thanks, Dad to the Bear. Well done.

This was spot on, fixed what appears to be a recently wide spread issue for High Sierra users.