Margin black around embed video (vimeo)

Hello,
I’m using wordpress 3.01 with a structure theme. Each time, i’m embed a video from vimeo :

<iframe src="https://player.vimeo.com/video/15981098?title=0&byline=0&portrait=0&color=ffffff&loop=1" width="600" height="338" frameborder="0"></iframe>

like this one, i’v got some big margin black in the top & the bottom of my video.
you can see it there :
here