XSL Get filename from URL

Question

I need to get just the filename from this url:

http://feedproxy.google.com/~r/TEDTalks_video/~5/XT8k_DqlzGc/KarenArmstrong_2009G.mp4

SO i need to get:

KarenArmstrong_2009G

I need the filename so i can add .jpg to it and another base url.