H ELECTRICITY
H04 ELECTRIC COMMUNICATION TECHNIQUE
H04N PICTORIAL COMMUNICATION, e.g. TELEVISION
21/00 Selective content distribution, e.g. interactive television or video on demand [VOD]
H04N21/40 Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
H04N21/41 Structure of client; Structure of client peripherals
H04N21/422 Input-only peripherals; , i.e. input devices connected to specially adapted client devices; , e.g. global positioning system [GPS]
H04N21/42203 sound input device, e.g. microphone