The issue of separate video & audio is quite common. My opinion is that it is something VDH could & should fix. But I'm just another layman. You can read up on the subject -- and many others, which I do recommend -- here:
Typically, when you see only certain resolutions on a web site, it's a choice made by the web site admins & devs. We mere peons are at their mercy. We can only take what they give us. If you have other tools that suit your purposes better in any given case, by all means use them instead of VDH.
I'd like to refer you to this other discussion. I must point out that it was contributed by other laymen so you, as a fellow layman, should be able to gain some knowledge from it.