@media attributes allow for specification of bitrates of the alternative video sources, so HTML5 probably already specifies all that is necessary to do bitrate switching. It even seems to me that Apple have already implemented it since [4] mentions the <video> element. But it might be a good question to ask on whatwg. Cheers, Silvia. [1] http://www.adobe.com/devnet/flashmediaserver/articles/dynstream_actionscript.html [2] http://www.longtailvideo.com/support/tutorials/Bitrate-Switching [3] http://www.iis.net/expand/SmoothStreaming [4] http://developer.apple.com/iphone/library/documentation/NetworkingInternet/Conceptual/StreamingMediaGuide/HTTPStreamingArchitecture/HTTPStreamingArchitecture.html#//apple_ref/doc/uid/TP40008332-CH101-SW2