CBR — Constant Bit Rate — is the simplest video encoding strategy: keep the bitrate constant. Every second of video uses roughly the same number of bits, no matter what's happening on screen. A calm dialogue scene gets the same bandwidth as a fight sequence with explosions. Predictable, easy to plan for, easy to provision a network around — and that's the whole point.
CBR is required in two real-world places. Live broadcast and IPTV, where the network was built around fixed-bitrate channels and the bandwidth simply isn't allowed to vary. Constrained-buffer playback, like satellite TV or older set-top boxes, where the decoder buffer is small and the bitstream cannot temporarily spike. For these, CBR keeps the engineering predictable.
The cost is that CBR is wasteful on most content. Easy scenes (a static talking head) get more bits than they need — the picture won't get any better. Hard scenes (snow, sports, explosions) get the same bits and end up looking worse than they should — they had less headroom. Modern alternatives — vbr, crf, capped CRF — vary the bitrate scene by scene and give noticeably better quality at the same average bandwidth. For VOD streaming, video-on-demand and most general-purpose use, CBR is the wrong default in 2026. It survives only where the channel or the regulator demands it.
