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
H04N21/43 Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
H04N21/439 Processing of audio elementary streams
H04N21/4394 involving operations for analysing the audio stream, e.g. detecting features or characteristics in audio streams