ONVIF Notifications

Having defined a motion detector rule I now want to receive notifications from my ONVIF ip camera.

ONVIF uses the WS-Notification standard for event distribution. This standard defines a publish-subscribe model that uses SOAP web service messages.

Using the same techniques described in earlier posts I created proxy modules from the WS-Notification WSDL files. Eventually I will upload all this code to my ZoneMinder branch on github.

Perl HTTP daemon

Up to now I have only queried my camera and then got a response immediately. For notifications to work we need a more complex setup:

1. Set up a local HTTP daemon to receive the notifications.
2. Register the daemon with the camera.
3. Wait for messages.

Since the ZoneMinder scripts use the Perl programming language I used the SOAP::Transport::HTTP::Daemon module to implement the daemon.

The daemon listens on a local port of my linux box.

Subscription

The camera now needs to know that we are listing. Therefore we send a Subscribe message specifying our local ip and local port to the camera’s ONVIF Event service. The message also contains the events we are interested in and the validity time of our subscription.

When we subscribe to events from the camera we get a response like this:

<wsnt:SubscribeResponse>
  <wsnt:SubscriptionReference>
    <wsa:Address>http://192.168.0.21/onvif/Events/SubManager_2014-09-08T16:19:23Z_0</wsa:Address>
  </wsnt:SubscriptionReference>
  <wsnt:CurrentTime>2014-09-08T16:19:23Z</wsnt:CurrentTime>
  <wsnt:TerminationTime>2014-09-08T16:20:23Z</wsnt:TerminationTime>
</wsnt:SubscribeResponse>

Comparing the CurentTime and TerminationTime tags we can see that the subscription is valid for only one minute in this example.

Renewal

Now what happens when the TerminationTime is reached? The camera then simply forgets about us and sends no more events our way.

Using a Renewal request we can extend the subscription time. Observe that we must send the Renewal request (and any other requests referring to the subsciption) to the subscription manager’s URL not to the ONVIF Event service. We got the subscription manager’s URL in answer to our Subscribe request above:

http://192.168.0.21/onvif/Events/SubManager_2014-09-08T16:19:23Z_0

Notifications

Now we are set up. If we wave a hand in front of the camera we should get a Notify message. Below I pasted an example from my camera:

<env:Body>
<wsnt:Notify>
<wsnt:NotificationMessage>
  <wsnt:Topic Dialect="http://www.onvif.org/ver10/tev/topicExpression/ConcreteSet">tns1:RuleEngine/CellMotionDetector/Motion</wsnt:Topic>
  <wsnt:Message>
  <tt:Message UtcTime="2014-09-09T12:43:39Z" PropertyOperation="Changed">
  <tt:Source>
    <tt:SimpleItem Name="VideoSourceConfigurationToken" Value="VideoSourceToken"/>
    <tt:SimpleItem Name="VideoAnalyticsConfigurationToken" Value="VideoAnalyticsToken"/>
    <tt:SimpleItem Name="Rule" Value="MyMotionDetectorRule"/>
  </tt:Source>
  <tt:Data><tt:SimpleItem Name="IsMotion" Value="true"/></tt:Data>
  </tt:Message>
  </wsnt:Message>
</wsnt:NotificationMessage>
</wsnt:Notify>
</env:Body>

In the message we also see a reference to the motion detector Rule I described in another post.

Actually I get more messages. The one I pasted has IsMotion=true. And when the motion stops I get another with IsMotion=false. If the time intervals defined in the trigger Rule are too small I even get several events per second when waving my hand.

In upcoming posts I will concentrate on passing these events to ZoneMinder.