want to allow subscription group rights to upload video files while all others can only upload images but not video.

Can't figure out how to configure in ACP. Help?

I'm not aware of a method to do this currently, as the restrictions for this are not member group based.

Admincp > system > posting > general -  currently they apply to all groups I'm afraid.

You could request this as a member group setting in our feedback section and/or have someone create a plugin to do so for now.