Quicktime plays only audio with no video on mp4

[djon41]

I'm trying to get the root of a problem that has cropped up recently with playback of certain videos in Quicktime.

I have a set of .mp4 h264 videos that I have been getting regularly from the same source for a couple years with no issues. Recently (the last few months) I have been having an issue where these videos will only show a black screen during playback, but will play the audio track just fine. Further, they will play back totally fine in VLC. They will also play fine on my TV if I Airplay them through quicktime to my Apple TV (4th generation). The little thumbnail preview video that shows up when I highlight the file in finder also plays perfectly fine. I have a touchbar MacBook Pro, and the frames show up just fine in the scrubbing bar on the touchbar. I've even noticed today that when I turned off Airplay in the middle of the video, it continued to play correctly on the computer until I skipped back, at which point it just played the audio with a black screen again.

Any ideas what this could be or how I can try to troubleshoot?

 

[inscrewtable]

I'm always coming across this crap, even old videos that were edited in QT7 and played fine suddenly say they are missing codecs but I've never be able to work it out, it is most annoying. It's almost certainly a missing codec but I've never discovered the solution. Sometimes old files which didn't open at some other time will decide to open later. What change? I don't know. Will keep an eye on this thread.