Some H.264 files play jittery in Quicktime?
 

I have been delivering SD tapes as h.264 MP4 files for a few years now. I am using Windows 7 and 10 machines. I capture as DV .avi files and then encode to h.264 MP4 files with Adobe Media Encoder (either CS 5.0 or CS 5.5). I have a preset I created for this purpose so that each file encodes exactly the same. But within the last two months, some people have started reporting that a small number of their files are playing jerky or jittery, while the others play fine. All of these people are using Apple computers. What I've found is that these problem files play fine in VLC and Premiere, but play jittery in Quicktime Player. Re-encoding from the captured .avi file doesn't work. I have to recapture the tape and then encode, and if I do it works fine. I haven't any idea what might be causing this problem. I'm hoping someone here might have an insight.

And you actually charge money for doing this?