As above, multimedia files, images, graphics, even some flavors of autocad, do NOT dedupe well or at all.
Resample the audio, or delete 1 second off the tail end of that file, and it gets resaved as a completely new file. Same goes for deleting a single pixel in an image, it's re-saved as a completely new image, with most all bits re-arranged.
You'll get better dedupe from office files, vmware, hyper-v, exchange, and other databases. But Multimedia... Not gonna happen anytime soon. The best you can hope for is single instancing, where if the file were saved to multiple locations.
Your best bet, is looking at cheaper storage for files like that, and use that as a primary tier. The Symantec FileStore soft appliance w/ hardware in terms of price is something like 60% the cost of NetApp with more performance for the same capacity.
