Never mind, I got it. Just needed to specify the dimensions of the video. Thought my original footage was 640 X 480, but it's 860 X 480. Problem solved.
I've tried everything, but I can't seem to solve the problem.
Tried pan & zoom, but in my case that doesn't help. Why? Because I need to stabalize the video in yt afterwards.
It's kinda shaky so when I stabalize it, you will see the black bars shake instead of the footage itself.
I also tried every dimension. At one point I thought it was the images I imported alongside the videos. The image dimensions are bigger than that of the video files. So I resized the images to make it fit for the video, but that didn't solve anything either. I'm stuck here and it's getting really frustrating, because I need to finish this for a project of mine.