So, I was almost done with my animation and wanted to test it. I pressed test movie but then in the player, the images were hugely out of scale. I mean, almost all of the video was visible only in the upper left first corner.
Strangely, this wasn't a problem when I used the play button to see the animation.
I tried to lock the scale to 1920*1080 or click match contents but this made it even worse.