You can host webinars on your event site by using the "Watch now" feature. Once you have set up a webinar you are able to set up the "Watch now" button to automatically check-in a user when it is clicked by that user. This allows you to track how many registered users actually attended the webinar - or at least accessed the video link.
To enable this, click the Registration tab and then the Options menu item. Under the Attendee Accounts section, ensure that the checkbox next to “Allow apps and websites to process attendee check-ins” has been selected.
To see which registrants accessed the video link and thus were checked-in, go to the Registration tab and then click the Attendees menu item. Check the "Arrived" column on the right-hand side of the screen. This will show if, and when, a registrant accessed the video link.
Note: The “Watch Now” functionality must also have been enabled for the Session Schedule or Event Information block.