The Vonage Video API allows developers to add video to their applications by providing a default UI or custom video elements for more control over the video elements. To publish video, developers need to disable the default UI and create a publisher with specific options, such as resolution and audio/video settings. The publisher then publishes into a session, which can be accessed through an event listener that retrieves the mediaStream from the published video element. For subscribers, similar logic applies, but with one key difference: they need to follow specific steps for mediaStreams in versions > 2.24.7. By using custom video elements and accessing their mediaStreams, developers can gain more control over their video conferencing applications and avoid some features tied to the SDK's video element.