HD video over IP does use more bandwidth than say VOIP or ordinary video over IP, but is not realy a bandwidth issue with "lags and mosaic" it is down to "QOS" Quality of Service". As video over IP uses UDP to transport the pic and sound over the internet, it has to have some sort of "QOS" to ensure the video and sound packets get priority over everything else.
This works fine on a corperate network, as routers are setup with special Vlans and has QOS in place to make sure the UDP packets get from the one side to the other in the same order and with minium/no delay.
However on the internet there are no such services on place at the moment esp for HD video over IP as ordinary video over IP still gets lags with sound and vision mismatch.
This will improve as BT rolls over thier new 21CN network
I am currently studying VOIP and video over IP (the cisco CCVP) - fantasic subject and it is the future.