Disable Video/Voice Chat Throughout Account

How can I do it? (for account, not campaign)

It is per campaign as there is no video nor voice outside of the campaign game itself. Each campaign exist separately with only a few things shared globally such as your art library, if you were a subscriber there would be some other features such as your character vault that are interconnected to all your campaigns.

Unfortunately you can't, as Pat has explained. You have to turn-off the voice/video in each campaign you enter, under the settings tab at the top-right above chat. If you turn it off on a campaign, that setting will stick each time you re-enter that campaign. I think that there is a Suggestion thread for this, but I'm unable to find it at the moment. If you are really concerned about it, a workaround would be to go into your computer settings and disable your mic & camera completely.