GOP (Group of Pictures)
Definition
The repeating sequence of I, P, and B frames in an inter-frame compressed video. GOP size (the distance between I-frames) is an encoder setting that affects file size, seek latency, and forensic detectability of editing.
- Frame types
- I (intra), P (predictive), B (bidirectional)
- GOP size
- Distance between consecutive I-frames
- Encoder-controlled
- Yes, an encoder setting
- Forensic relevance
- Affects seek latency and detectability of edits
Common questions
Why does GOP size matter when detecting video tampering?+
Because I-frames carry complete image data while P and B frames only encode differences from neighbouring frames, an edit that disrupts the expected GOP pattern, such as an unexpected extra I-frame or broken sequence, can be a signal of re-encoding or splicing.
How does GOP size affect video file size and seeking?+
A longer GOP with fewer I-frames produces smaller files because more frames rely on compressed differences rather than full images, but seeking to an arbitrary point becomes slower since the player must decode back to the nearest preceding I-frame.
Is GOP structure the same across all video sources?+
No, GOP size and frame-type pattern are set by the encoder and vary between cameras, software and recording settings, which is part of why GOP structure can also help identify the encoding source of a video file.
Related terms
- Codec
- A coder/decoder algorithm that compresses and decompresses media data. H.264/AVC and H.265/HEVC are the dominant video codecs; AAC and MP3 are dominant...
- Container Format
- A file format (MP4, MKV, MOV, AVI, MXF) that multiplexes video, audio, and metadata tracks into a single file with a defined...
- I-Frame
- An intra-coded frame: a self-contained image compressed without reference to any other frame, like a JPEG. I-frames are the only random-access entry...
- Perceptual Coding
- Lossy compression that exploits psychoacoustic or psychovisual masking to discard information the human senses are least sensitive to. MP3, AAC, and AC-3...
- Rewrapping
- Moving a compressed bitstream from one container to another without decoding it. Forensically equivalent to the original encoded stream; no new generation...