download youtube vid opens in new window

i've been downloading youtube videos with safari by opening the activity window and double clicking on the largest file. usually this works fine, but sometimes it opens up in a new window instead of downloading to my computer. is this because of a certain format it's in or am i doing something wrong? and is there any other way i can download these types of videos?

thats what happens when you click it normally, not option click. its fine.

Moved to more appropriate forum.

ok yes thank you. however, try downloading this one: YouTube - Asteroid Computer Animation i can't get it to work

hold option and download the one with %Asteroid %Computer % animation at the end. i downloaded it easy.