This destroys nothing. Place it somewhere near the corners or over the point-table (there it's uncuttable *g), only hardly to recognize, but still there. If you want.
Ok, rsosa, you can listen to this person if you want, but be warned, if you do the things above, you will lose fans, because the only thing cool about your videos is that they showed originals, you will lose that cool if you put something stupid on it like PWDtennis, Top10tennisnetwork, Craigrena. I want you to know that I will fight for you and stop these motherf**king uploaders on youtube that are stealing your credits, you will have me and more people stand by you, but if you did the watermark thing, it is going to ruin you videos to be honest