picture is trembling - Marvel G400

[Speed Pete]

I hope "tremble" is the correct expression? But I'm sure, you can imagine what I mean.
The Problem: when I play a videotape and look at it via composite with my marvel then the picture is trembling. Not the whole picture, but only about one tenth at the top. The video looks fine, when looking at it directly on TV.

[This_Idiot]

Try searching for "overscan" and see if this matches up with your symptoms

[Speed Pete]

Hmm... I think this overscan is another thing. What is trembling here are not some Lines that are not visible on the TV, but a part of the movie wich is visible and stable on the TV.