Mysterious Gray Pointers

Hello, I've got something weird going on. I imported a video clip, and it came with these strange indicators embedded in it on my timelime. I can't move them, I can't grab them, and I can't seem to do anything at all with them. And I suspect they're the reason that my video won't export at full length, but rather as a single frame.
I tried deleting, saving, and then reimporting the video several times, but each time the indicators are there. Not sure what's going on! Any advice?
Can someone help me out?
