For example, Howard uses this language when he introduced the dragon shout concept:
But the big hints are here:
and here
So we know that the dragon shouts are simple, made up of three words which (at least in the paragraph describing them in-game) are short and monosyllabic (FUS, RO, DAH!) - and therefore, would be easy to remember. We know that that certain shouts must be spoken in a certain way, and Howard also suggests the importance of proper diction to the success of the shouts. Those latter two details seem particularly irrelevant if the dragon shouts are simply activated with a button press like any normal spell. My theory, then, is that the player himself will be speaking these words of power to form the dragon shouts, through a headset or a microphone connected to their gaming device.
I don't think this will be the only way to activate the shouts. There will almost certainly be some backup method using button presses, for the sake of the hearing impaired and those who'd feel too self-conscious yelling dragon language at their televisions. Alternatively, they may use some sort of unique in-game activation method, something like the Legend of Zelda series uses for the ocarina or Wind Waker baton. And of course I could be way off and the shouts are just assigned a button like any spell or attack.
The question I'd like to ask, though, is how you'd feel about using your voice to empower your character. Do you think such a feature would be beneficial to immersion, or too jarring and would pull you out of the experience? And there's the fear that, if not implemented properly, shouts could be frustrating and difficult to pull off. Or, if the game doesn't actually have this feature, would you be interested in a mod that added it?
Share your thoughts, denounce me as a fool, whatever you want. Speculation is fun