HELP! Podcast videos not working.

Hey guys.
I subscribe to TED podcasts and they are automatically downloaded onto my microsd on my Bold 9900. Most of the podcasts are videos and I'm using the standard Blackberry podcast (fully updated). The problem is, some of my TED videos dont work in the middle. The video starts off fine and after maybe 3 to 5 mins, the video freezes and a message pops up saying that this video format is not supported by Blackberry (which is surprising since it plays the first couple of mins well). This doesnt happen with all the podcast videos though (maybe 1 in 5 problems). Can anyone help?
Thanks.