How does AVOD ad-serving work technically ?

AVOD is a random interruption of a video playback, triggered by an ad-server which then calls on demand-sources (Ad Networks, Exchanges, VOD Channels, etc…) to see if an ad is available and then, if an ad is available, the ad-server serves the ad into the video player. Then once the ad has been played (or skipped if the player allows that), the video resumes where it left off. 

This AVOD process is not compatible with existing empty pauses in a video. Instead AVOD creates its own breaks by calling on demand sources periodically, pausing the playback of the video, serving the return ad into the player and then resuming the video playback in the player.

More information can be found at: 

https://help.lightcast.com/how-to-monetize-your-videos-using-avod

https://help.lightcast.com/is-it-possible-to-switch-ad-feeds