The Impact of GOP Size on Video Quality

This freely downloadable report measures the qualitative impact of GOP sizes on animated, general entertainment, sports, and office footage for H.264 and HEVC.

The impact of GOP size on VMAF quality
The impact of GOP size on VMAF quality. Click to view at full resolution.

One of the most fundamental encoding decisions is GOP size or the frequency of I-frames in our encoded files. I-frames, also called keyframes, start each “group of pictures” comprised of I-, B-, and P-frames. Most of the time, our GOP size, or I-frame interval, is dictated by adaptive bitrate considerations like choosing a GOP size that divides evenly into your segment size. But even then, you have multiple options. In addition, what GOP size should you use when encoding a single file for disk-based playback or progressive download?

This report helps you decide. It measures:

  • VMAF quality
  • Of 13 files in four genres (animations, general entertainment, sports, office)
  • With keyframe intervals ranging from 1/2 second to 20 seconds
  • Encoded with x264 and x265

No registration is required; click here to download the report. GOP-Size_report_11_16.pdf (652 downloads )

About Jan Ozer

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I help companies train new technical hires in streaming media-related positions; I also help companies optimize their codec selections and encoding stacks and evaluate new encoders and codecs. I am a contributing editor to Streaming Media Magazine, writing about codecs and encoding tools. I have written multiple authoritative books on video encoding, including Video Encoding by the Numbers: Eliminate the Guesswork from your Streaming Video ( and Learn to Produce Video with FFmpeg: In Thirty Minutes or Less ( I have multiple courses relating to streaming media production, all available at I currently work as as a Senior Director in Marketing.

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