Multimedia Mike has ported the "youtube codec" VP8 over to the Dreamcast!.
"So, can the Dreamcast decode VP8 video in realtime? Sure! Well, I really need to qualify. In the test depicted in the picture, it seems to be realtime (though I wasn’t enforcing proper frame timings, just decoding and displaying as quickly as possible)."
Maybe somebody can implement that into one of the browsers so we can watch youtube on our Dreamcasts ^_-.