Why do humans need real-time video communication on Mars? It won't be real-time. Mars is 3 light-minutes away from Earth. The best we can hope for is a 6 minute lag between you asking a question and getting an answer.
And if you're going to have a six-minute lag, pretty much the bandwidth is irrelevant. It might as well be by the cheapest way possible, i.e. audio only with the occasional static picture for the "What the hell is this in the microscope?" questions.
The sheer bandwidth is also the problem. At 6 minute latencies, you're basically introducing more and more "buffers" to ensure correct data transmission. You won't know if what you sent was received properly until six minutes later. So you have to store AT LEAST six minutes of data (more likely lots more as you will have to retransmit).
The more bandwidth you wish to buffer, the larger storage that six minutes costs you. Six minutes of audio is nothing. A few hundred Kb. Six minutes of video is more. Six minutes of HD video is more again. And so on. And everything that you store / forward costs BIG money over interplanetary scales - from the broadcasting station itself (which can't reasonably ever be upgraded) to the DSN satellies around Mars to the receiving stations on Earth, and the more you send and the more you store and the faster you want to do it, the more it costs EVERYWHERE.
And, as you state, there is NO scientific value in this. So until humans are on the planet, it's really moot. But once they are there, HD video is the least of their concerns.
This is probably why you're not Director of Planetary Exploration at NASA, by the way.