My daughter sends me 20-30 second videos of my grandchildren that she takes with her iPhone. I have a PC but have downloaded QuickTime, which should enable me to play the videos. The audio comes through fine but the video doesn't play unless I repeatedly click on the two "back" arrows (<<) while it's playing, and even then it's jerky and misses things.
Any suggestions on what I can try, other than getting a Mac?
Are you sure you have the latest verison of Quicktime? That's the only thing I can think of: the iPhone may have a different codec or newer Quicktime version.