Glossary A–ZLetter B
Bit rate
Bit rate states how much data a video or audio track contains per second, usually in megabits per second (Mbit/s).
Together with the video codec, it determines picture quality and file size.
Bit rate matters to screen networks for two reasons. First, file size grows with it: size is bit rate multiplied by running time, so a 60-second film at 10 Mbit/s is about 75 megabytes. That counts when transferring over mobile networks and for storage on the player. Second, the player must be able to decode that amount of data in real time. If the bit rate is too high, the picture stutters or freezes. A distinction is made between constant bit rate (CBR) and variable bit rate (VBR), where calm scenes receive less data and busy ones more.
A higher bit rate improves the picture only up to a point; after that only the file grows. Operators should be guided by the screen's resolution and convert videos to suit it, rather than distributing files straight from the editing software. With streaming, the bit rate also determines how much bandwidth is needed continuously.