The video zoom works only when the video feed is active. You can adjust the zoom to your liking by using two fingers. The zoom stays saved until you change the orientation of the screen or stop the monitoring session.
As a default, the video feed is set to fill the screen. We have added an option to fit the video inside the screen for users with custom devices or users who want to view only a certain part of the monitored area. You can change this setting from the menu on the active Person Station (Menu -> Settings -> Video settings -> Display mode -> toggle zoom to fill off (or choose the desired setting on Android). You can adjust the video size the same way you can zoom (described in the paragraph above).