@DieterK has added that functionality to the IP Camera binding and we are just waiting for a PR to be done, you can read his post here on it…
Onvif camera error message - Add-ons / Bindings - openHAB Community
It is far better to use the ONVIF methods as they are event based and the events get pushed to the binding, where how your doing it with the http binding is polling and not as good as event based methods. If you place the binding into DEBUG level logging it will tell you if the camera is reporting events that the binding does not have implemented and if you post this info, it can be added very easily.
@azureshammer Let me know when your able to compile the code and create a jar. I think the best way forward would be to use ONVIF if the dvr channel is 0, and for numbers above this, it could switch to polling so people get the best of both worlds. But this requires someone to test that actually has a camera. I would not be surprised if the API polling has added benefits and extra features. For example with Dahua and Hikvision if you get a Line Crossed alarm, the API can tell you which direction the line was crossed so you know if someone if walking towards or away from your home.