Compression markers (i-frames) - newbie question ?

I've got a scene with a lot of motion and I need it to be not compressed so much.

I am in Compressor and have added a compression marker at the beginning of the scene.

My question is, after the marker, how long is it valid for? Ie: Does it tell compressor to give a high quality output for 10 seconds, or until I put in another marker (between marker 1 and 2 )?

Or does Compressor think,"when I see a compression marker, I do not compress for the next 30 frames"...?