I hit 700MB RSIZE after doing "play all" on the videos at the URL, then closing all windows. It looks as though the ram usage grows steadily as the video streams, and then doesn't get returned to the system once it's done.
Using the r21432 nightly on 10.4.9/x86
I can reproduce this. I tried in both release and debug builds of WebKit. 'leaks' indicates no leaks that it could detect.
No obviously relevant leaks I should say. There are a few minor leaks that appear to stem from other components of the OS.
Camino seems to handle this a lot better. Loading the first video on the page increases RAM usage by roughly 320MB, which is all deallocated once the window is closed. In my mind this rules out bad behaviour inside the Flash plugin itself as the cause of the memory use sticking around.
Running Version 3.0.3 (522.12.1) I find that long Google Videos exhibit the same leaky behavior over time. In particular, I played this video for ~45 minutes and by the time I went to stop the video, my system was nearly at a stand still:
Fixed with r28006.
*** Bug 16377 has been marked as a duplicate of this bug. ***