Publitio looks to optimize bandwidth usage by streaming it in chunks (small parts) that buffer in the player.
Bandwidth is consumed by each view that was requested.
Images are simple to understand if an image is 100kb it will consume 100kb of bandwidth when you view it.
Every time video is played it will consume a portion of bandwidth, and if the video has 1000mb it will start streaming it to user (downloading) and during that time it will start calculating how much of 1000mb was downloaded (100mb is for example 10%) and if a user watches only part of the video and closes the page before 1000mb was downloaded your account will calculate usage as 100mb or how much it was actually downloaded, not 1000mb.
If the user has high-speed internet and 1000mb can be streamed (downloaded) in 5-10s no matter how many minutes of a video he watched if he downloaded all 1000mb we will calculate it as 1000mb in bandwidth.