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What is VBR (variable bitrate)?

VBR (variable bitrate) is an encoding mode where the encoder spends more bits on complex frames and fewer on simple ones, instead of allocating the same budget to every second. The result is better visual quality at the same average bitrate, at the cost of unpredictable file sizes. YouTube's encodes are predominantly VBR.

Also called:variable bitrate · vbr encoding

CBR (constant bitrate) gives every second of video the same byte budget regardless of content. A static talking-head shot gets the same allocation as a fast-cut explosion sequence — meaning the talking head is overspent on and the explosion is underspent.

VBR fixes this by letting the encoder peek at upcoming complexity and allocate adaptively. The total file size is similar to a CBR encode at the same average bitrate, but the visual quality is more uniform — fewer ugly frames during the action sequences.

For streaming services with adaptive playback, VBR is universal. CBR is mostly used for live broadcasts where bandwidth caps are strict.

Common questions

Is VBR always better than CBR?
For visual quality at a given file size, VBR wins almost always. For predictable file size or strict bandwidth budgets, CBR is more controllable.

Related terms

Bitrate

Bitrate is the amount of data a video or audio stream carries per second, measured in bits per second (bps) or kilobits (kbps) and megabits (Mbps).

Codec

A codec is the algorithm that encodes (compresses) and decodes raw audio or video into a smaller stream.

Transcoding

Transcoding is the process of decoding a compressed media file and re-encoding it into a different codec, container, bitrate, or resolution.

VidPickr is a free, browser-based YouTube downloader. Every term in this glossary either describes how YouTube delivers video or why your downloads behave the way they do. Try the downloader →