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?