How can I subscribe to an event of start recording? I want the user to fill a form before any recording he wants to start.

I think you can see it on NewEventIndication, if i am right you will be able to see this in the StausViewer sample.

This is on XProtect Corporate, Expert and the new Plus versions. There is no event in the XProtect Enterprise, Professional and Express.

In the XProtect Enterprise, Professional and Express you can use the ImageViewerControl and then see the status information on

virtual LiveStreamInformationHandler VideoOS.Platform.Client.ImageViewerControl.LiveStreamInformationEvent

but this means you must be streaming live images.

Now if the recording is only happening on user interaction it might be easier to ask to user to fill a form and then order the recording..