Autofocus in video mode

I'm a rank beginner when it comes to shooting video with a DSLR. I first tried it when I got my D90 9 years ago, but that camera didn't offer AF in video mode. I shot some video thinking I'd gotten the focus right, but when I viewed the results I saw that I hadn't. So, I gave up on using the D90 for home movies.

Fast forward to this year. I was really looking forward to trying out DSLR video again now that I had the D7200, but once more I'm disappointed. The images are initially in focus, but if the subject moves toward or away from the camera focus is lost. I've got the camera set to continuous autofocus...why isn't it adjusting as the camera-to-subject distance changes? Am I missing something here?

Thanks for any help.

There are many video tutorials on setting the various focus modes for video with that camera. AF-C is NOT the same/only setting you need for continuous focusing in video. Just from a videography standpoint, DSLRs and continuous focusing is problematic from the standpoint of focus speed and the internal proximity to the mic. It's slow and noisy... Video lenses typically are smoother, quieter, and manual... It's called "pulling a focus"...shots are planned and focus changes are done manually...

AF for video is just starting to become of use but i think you will find it mainly in the more expensive video aimed mirrorless cameras like the Panasonic G5 but your talking around £1500, I would look into what Fred said above.