There may be several problems you're having. The first one is the sequence settings if you haven't started it to your best advantage, an additional one if you've not got your "Source" track targets set properly.
For the first one, what is your sequence for framerate and framesize ... 24fps, 29.97, what? ... and 1280x720, 1920x1080, what?
What is your video media framerate and framesize?
Next, make sure that you have Source track targets set ... the farthest left blue blocks here ...