You can't directly link an object to a specific line of text that's scrolling, but it's pretty simple to use keyframes for the moving object to sync it up.
You can place a timeline marker at the start and end of the window where that text line enters and leaves the frame, then trim your media clip to those locations. If you want it to scroll in from the bottom, use the PiP Designer's keyframes to set the clip's starting position there and then set the ending keyframe with the object just past the top of the screen.
You can have the clip's size rotation, opacity and location fixed the entire time or you can change it at any point (or points) along the way.
One thing to keep in mind is that if you make any changes to the
duration of the scrolling text or add/delete
any lines of text (not including changing any individual characters or the contents of an existing line), then the scrolling speed and timing will change and you'll need to reposition the tracking clip on the timeline and/or adjust its duration.
This is all straightfoward, so check out any keyframe tutorial if you have any questions on how to do this, and also for more ideas on what can be accomplished if you're interested in "animating" your clip.
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