As far as I understand, ONVIF only supports video streaming, right? Other functions, such as changing resolution, frame-rate, quality, brightness, motion detection, input signal, output relays, or PTZ aren't defined in ONVIF.

Actually this is wrong. For example:

• In Imaging WSDL specification, command SetImagingSettings is defined to change Brightness, Contrast, ColorSaturation, and Sharpnes.
• In Media WSDL specification，command SetVideoEncoderConfiguration is defined to change Encoding(Codec), Resolution, Quality, FrameRateLimit, and,BitrateLimit.

Other functions, such as motion detection, input signal, output relays, and PTZ are, in fact, well-defined in the corresponding specifications.

Such misunderstandings can be traced back to the early stage of ONVIF development. At that time, merely supporting video streaming can pass ONVIF test tool and thus declare ONVIF comformance. To simplify matters, most vendors choose to implement only video streaming. All these start to change recently.