What is in the ONVIF Standard?
The ONVIF Specifications cover things like IP configuration, device discovery, device management, PTZ camera control, and video analytics.
Working in parallel are ONVIF Profiles. Profile C is for IP-based access control; Profile G is for edge storage and retrieval; and Profile S is for IP-based video systems.
Do You Have to be ONVIF Compliant and Profile S Compliant?
It is not possible to be ONVIF compliant only; you need to be compliant to a Profile as well. You can be ONVIF conformant only, but if you are it is not guaranteed that you would get interoperability between other ONVIF devices and clients. (This is why cheap ebay cameras are not really "Onvif")
What Does it Mean to be ONVIF Compliant?
It means that you will have the confidence that your product, be it client or device, will work with other products certified at the same level. For example, a Profile S device can be expected to work with a Profile S client.
Why ONVIF does not always work?
First, it is necessary to check whether intended devices actually support ONVIF protocol.
Second, it is important to use ONVIF devices with the same profile. For example, a camera compliant with older version of ONVIF protocol (without profiles) will not connect to a DVR with the higher version.
Read more about ONVIF at: https://www.onvif.org