You can actually do this today. Simply change your encoding parameters to a higher bit rate and larger resolution. Then, upgrade your flash player from the default included with vShare to version 4. When someone watches a video, the player will stream at HD. If they choose to watch lower quality, they can click on the player and choose "Low Quality." The player will then down convert the video automatically. Technically, "HD" is nothing more than a higher bit encoding rate (so that there is less lost picture) and a higher resolution (in TV terms, from 640 x 480 to 1280 x 720 minimum) so you really only need one source (the highest resolution). From there, the player can control the playback. This is how all of the tube sites with high-quality video do it.