VBR — Variable Bit Rate — is the rate-control mode that lets the encoder spend more bits on complex scenes and fewer on simple ones, while still hitting a target average bitrate over the whole video. A 5 Mbps VBR stream might use 12 Mbps during a fast-moving fight scene and 2 Mbps during a static dialogue, and on average it works out to 5. The result is dramatically better quality than cbr at the same average bandwidth.
VBR comes in flavours. Single-pass VBR lets the encoder make on-the-fly decisions about where to spend bits — fine for live, but it doesn't know what's coming next, so the distribution isn't optimal. Two-pass VBR analyses the entire video in a first pass, then encodes in a second pass with full knowledge of which scenes need more bits and which need fewer; the result is noticeably better at the cost of doubling encoding time. For commercial VOD libraries, two-pass VBR was the industry default for years.
In 2026, VBR is being squeezed from two sides. For VOD, crf and capped CRF are usually preferred because they target visual quality directly rather than bitrate, producing more consistent perceived quality across a library. For live and ABR streaming, capped VBR (VBR with a hard maximum bitrate) wins because it gives bandwidth predictability for the CDN while letting the encoder still vary bits scene by scene. Pure unconstrained VBR survives mainly in archival, broadcast contribution, and pipelines built around tight average-bitrate targets.
