Genvid uses a Commands Channel to communicate between an application and the game. It allows an application to send commands to the game and influence it directly.
Using Unreal Tournament 4 as an example, you can have the broadcaster affect the environment during a match by selecting a different loot drop location or closing off sectors of the map to increase difficulty.
Commands are independent from events and should not be used for viewer input. Commands send input to the game directly and are not scalable. You could, however, use the results of events to help determine what commands the broadcaster should send.