I have no idea what could be cause this.
Is that a single video or is there one video or graphic overlaid onto another? Two or more separate tracks of video?
Can you post a screen capture of your timeline at this point so we can see what it looks like?
What model of camcorder is your original video coming from and what format and resolution is it?
It appears this video may be from a source other than a camcorder -- possibly ripped from a DVD or copied from YouTube. If so, that opens a whole other realm of possibly as either the video may have copy protection built into it or the software you used to ripped the file may be creating something other than a standard video file.
I think it's two separate tracks of video/audio, there's the photo if that helps/is what you're looking for, both videos were ripped off of YouTube using this site.
Note: I did edit the explosion a bit so that there was solely the green screen part.
And thanks by the way! Again I just got it and I'm a complete novice so it is felt really great to see that someone had responded.
I really don't feel qualified to answer with regard to videos ripped from YouTube, Bluebomb. I'm not sure what that site is doing to your video or if the videos are using constant or variable frame rates or even if that site is adding malware to your computer.
Maybe someone else with experience using that site's software has some suggestions.
Alright, thanks for taking the time to answer though! I'll experiment with some other sites that I've heard to be reliable. I'm sure I can find something that works.
From what I see is the problem in the videos in the links you have shared. There are vertical black bars in the first video and there is none in the second. When you add a clip in PRE, PRE creates a project whose settings matches closely with the first clip. Any clip you add later and if dimensions are not proportional to Settings then PRE adjusts them to match. One issue could be that those black bars are part of the video clip you imported to PRE, the other could be that dimensions are not matching.