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Glossary · metric

What is GOP length (keyframe interval)?

GOP length is the duration between keyframes in a video. Short GOP (1-2 seconds): fine-grained seeking, faster recovery from packet loss, larger files. Long GOP (10 seconds): smaller files, coarser seeking. YouTube uses ~5-second GOPs as the trade-off.

Also called:keyframe interval · gop size · i-frame interval

See [/glossary/gop](/glossary/gop) for the introduction. This entry covers the trade-off space deeper.

GOP length directly affects three things:

- Seek granularity: lossless cuts can only start at keyframes. 5-second GOP = ±5s precision for lossless clips.

- File size: shorter GOP = more keyframes = bigger files (keyframes are 5-10x larger than P-frames).

- Streaming resilience: shorter GOP recovers from packet loss faster. Live streaming uses 2-second GOPs; VOD uses 5-10 seconds.

YouTube's 5-second GOP is a balanced choice — fine enough for most clip / share use cases, long enough to compress efficiently. Lossless clips from YouTube downloads can start at any multiple-of-5-seconds boundary; finer precision requires re-encoding the clip start.

Common questions

Can I extract a perfectly-timed clip from YouTube?
Lossless clips snap to GOP boundaries (every 5 seconds in YouTube's case). Frame-accurate clips require re-encoding the clip start, which adds a small generation of quality loss. For most uses, lossless 5-second-aligned is good enough.

Related terms

GOP (group of pictures)

A GOP (group of pictures) is a sequence of video frames that starts with a keyframe and continues with frames described as differences from earlier frames.

Keyframe (I-frame)

A keyframe (I-frame) is a video frame that stores a complete picture, independent of any other frames.

Codec

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

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