What Is Video Bitrate?
Bitrate measures how much encoded data a video uses per second, usually expressed in kilobits or megabits per second.
Bitrate and file size
At a fixed duration, doubling total bitrate roughly doubles file size. Audio bitrate counts too, although picture data usually dominates.
Why one number does not fit every video
A static slide can look clean at a low bitrate. Confetti, foliage, game footage and camera noise are harder to describe and need more data.
Constant quality or target bitrate?
Constant-quality modes let size vary to maintain a visual level. Target bitrate modes are useful when a file must fit a known limit.