What is a GOP?

GOP" stands for Group of Pictures. A GOP refers to a sequence of consecutive frames in a video stream that includes one keyframe (I-frame) followed by a series of non-keyframes, which can be P-frames (predictive frames) and B-frames (bi-directional frames). The keyframe within a GOP serves as the reference point for decoding and displaying subsequent frames within that group.

Here's how a GOP is structured:

Keyframe (I-frame): The GOP starts with a keyframe (I-frame), which is a complete and self-contained frame that does not depend on any other frames for its display. It serves as the anchor or reference frame within the group.

P-frames (Predictive Frames): Following the keyframe, P-frames are included in the GOP. P-frames are encoded by predicting the differences between the current frame and the previous reference frame (which could be a keyframe or another P-frame) and then applying motion compensation. They rely on the keyframe or other reference frames for reconstruction.

B-frames (Bi-directional Frames): B-frames come after P-frames in the GOP. B-frames are encoded by predicting the differences based on both previous and future reference frames. They provide higher compression efficiency but require more complex decoding.

The grouping of frames within a GOP allows for efficient video compression. By including non-keyframes (P-frames and B-frames) that only encode the changes or differences from reference frames, the overall file size can be reduced while maintaining video quality.

The size of a GOP, also referred to as the GOP size or keyframe interval, is determined by the number of frames between consecutive keyframes within the video stream. A smaller GOP size (more frequent keyframes) provides better random access and error resilience but may result in larger file sizes. Conversely, a larger GOP size (less frequent keyframes) improves compression efficiency but may reduce random access capabilities.

In summary, a GOP (Group of Pictures) in video streaming is a sequence of frames within a video stream. It starts with a keyframe (I-frame) and is followed by non-keyframes (P-frames and B-frames). The keyframe acts as the reference point for decoding and displaying subsequent frames within that group. GOPs are essential for efficient video compression and playback.