AM3 Processors aren't being discontinued, where did you read that?
But since your encoding and not gaming it is better that you got the X6.
It was on AMD's roadmaps that Athlon II/Phenom II would be EOL by the beginning of 2012. Here's an article that they're done taking orders for them end of year, supply will dwindle in the coming months. http://news.softpedia.com/news/AMD-to-EOL-45nm-Phenom-II-and-Athlon-II-CPUs-in-Q4-2011-223974.shtml
I don't know why anyone would expect AMD to continue making 45nm AM3 chips when they've now launched their entire 32nm line up from budget FM1 to high end AM3+.