# What are B-Frames?

B-frames are bi-predictive video frames that may use earlier decoded pictures, later decoded pictures, or both as references. This flexibility can improve compression efficiency over one-direction prediction.

Video + audio tracks

Video processing

Playable derivative

Video processing decodes timed tracks, transforms them, and encodes a deliverable for a target player. This diagram shows video broadly, not specifically B-Frames.

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## How B-Frames work

A B-frame can predict picture data from either or both of its reference lists, which may identify decoded pictures earlier or later in display order. When it uses a later picture, that reference must be decoded first, so coded order may differ from presentation order. This improves compression opportunities but creates reordering buffers and latency. Encoders tune B-frame count, reference structure, and hierarchy according to delivery latency, decoder capability, and random-access requirements.

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## Key facts

1. 1Containers or elementary streams carry decoding and presentation timing needed to reorder pictures; treating packet order as display order can produce incorrect playback.
2. 2Hierarchical B-frame structures can make some B-frames references for others, improving efficiency but increasing dependency depth and error propagation when data is lost.
3. 3Low-latency encoders may disable or limit B-frames because future-picture prediction requires lookahead and decoder buffering, even when the codec otherwise supports them.

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## When B-Frames matter

Increase B-frame use when smaller files or higher quality at a given bitrate matter more than minimal latency. Some workflows limit them because they add reordering delay, memory demand, or decoder constraints.

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## Common use cases for video

These examples cover video broadly, not specifically B-Frames.

* Preparing uploaded video for web, mobile, connected-TV, social, or editorial playback.
* Creating clips, thumbnails, captions, alternate aspect ratios, and adaptive renditions.
* Normalizing camera, screen-recording, and user-generated files into predictable outputs.

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## Working with video

This guidance covers video broadly, not just B-Frames.

A demuxer separates tracks from the container, decoders turn compressed streams into frames or samples, and filters apply spatial or temporal changes. Encoders compress the transformed tracks before a muxer writes the chosen output container.

Video compatibility is the product of codec, container, profile, level, frame rate, color, audio, and subtitles. Validate the complete output on target devices because a playable file on one decoder may fail or look different on another.

### What you gain

* Standardized derivatives make diverse source files playable on target devices.
* A retained master can feed many resolutions, aspect ratios, codecs, and channels.
* Automated inspection and transformation make large upload volumes consistent.

### What it costs

* More efficient codecs can lower bitrate at similar quality but usually cost more compute and may have narrower support.
* Higher resolutions and frame rates preserve more detail and motion while increasing processing and delivery requirements.
* Fast encoding settings improve throughput but can produce larger files or lower quality than slower analysis.

### Before production

1. 1Inspect codec, container, dimensions, frame rate, color, audio, and subtitle tracks.
2. 2Test visual quality and playback support across the slowest and oldest target devices.
3. 3Preserve a suitable master before applying lossy, destructive, or delivery-specific changes.

[← AVOD](/glossary/avod.md)[Batch Queue →](/glossary/batch-queue.md)

More in video

* [2160p](/glossary/2160p.md)
* [Asynchronous Video](/glossary/asynchronous-video.md)
* [AV1](/glossary/av1.md)
* [Bitrate Control](/glossary/bitrate-control.md)
* [Bumper](/glossary/bumper.md)
* [CBR vs. VBR](/glossary/cbr-vs-vbr.md)

[All 505 terms](/glossary.md)

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