What is a keyframe interval (GOP size)?

A keyframe (I-frame) is a complete image frame in a video stream. The GOP (Group of Pictures) size is how many frames sit between two keyframes. A GOP of 60 at 30 fps means one keyframe every 2 seconds.

Why does keyframe interval matter for streaming?

HLS and DASH segment streams at keyframe boundaries. If your segment length is 2 seconds, your GOP must also be exactly 2 seconds (or a divisor of it) so players can seek without decoding garbage frames.

What keyframe interval should I use?

For streaming (HLS/DASH/Twitch/YouTube), use 2 seconds. For video-on-demand files where seek accuracy matters more, 1–4 seconds is common. For archival or editing masters, a larger interval (10–15 s) reduces file size at the cost of seek precision.

Does the GOP have to be a whole number?

Yes — encoders require an integer frame count. This calculator rounds to the nearest integer and shows you when the result is not exact so you can adjust your frame rate or interval accordingly.

What is the FFmpeg flag for GOP size?

The flag is -g . For example, a 60-frame GOP at 30 fps is: ffmpeg -i input.mp4 -g 60 output.mp4. You can also force keyframes every N seconds with -force_key_frames "expr:gte(t,n_forced*2)".

Keyframe Interval Calculator

Name: Keyframe Interval Calculator
Availability: InStock
Author: Nham Vu

Enter your frame rate and desired keyframe spacing to get the exact GOP size for your encoder.

Encoding Parameters

Frame Rate (fps)

Seconds Between Keyframes

Common targets: HLS/DASH streaming = 2 s • Broadcast = 1 s • VOD scrubbing = 2–4 s • Archive/edit = 10–15 s

GOP Size (keyframe interval)

frames • every 2 s at 30 fps

FFmpeg flag

-g 60

GOP at common frame rates

FPS	GOP	Exact?

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Summary

Enter your frame rate and desired keyframe spacing to get the exact GOP size for your encoder.

How it works

Enter your video frame rate (e.g. 24, 30, 60 fps).
Set the desired seconds between keyframes (2 seconds is standard for streaming).
The calculator multiplies frame rate by the interval to get GOP size.
Copy the GOP value and paste it into your encoder settings.
Use the FFmpeg or HandBrake command snippet shown below the result.

Use cases

Setting the correct GOP for HLS/DASH adaptive streaming.
Configuring OBS or streaming software for low-latency broadcast.
Calculating keyframe spacing before exporting from a video editor.
Optimizing scrubbing performance for video-on-demand files.
Verifying encoder settings match a delivery spec (e.g. 2-second GOP).
Comparing GOP sizes across common frame rates at a glance.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu