thanks for the answer !
Just how can i do that ^^' ?

Hi everyone, I wanted to use a portal 2 for a video but there's a lot of white lines wich is really, annoying http://www.youtube.com/watch?v=YmwnKVeTv3A&feature=youtu.be I tried to uncheck the draw game entities/world brush models , it worked, but it remove the ground too. How can i remove it?
(Thanks for your attention.)