Constant bitrate holds a stream at a fixed data rate regardless of scene activity, padding quiet footage to keep the rate steady. Networks and storage are easier to size because the peak is known, but an empty scene uses more space than it needs and the ceiling can limit detail in busy scenes.
Constant bitrate is a planning convenience as much as a picture setting. It trades efficiency for predictability.
Why constant bitrate is predictable
A fixed rate reserves the same capacity on the link and writes the same volume per hour, which makes storage and network sums simple and conservative. That predictability suits sites where the network is shared, or where the recorder’s throughput is already close to its limit.
Where it wastes capacity
A camera watching an empty corridor overnight still uses the configured rate. Across many cameras that is real disk space, and the trade is only worthwhile where activity is genuinely steady. Compare the figure with the average a variable setting would produce before committing.
Related:Glossary: NVRGlossary: VMS