A GOP (group of pictures) is the structure of frames between one keyframe and the next: an independent I-frame followed by predicted P- and B-frames that only store the differences. Longer GOPs compress better (fewer expensive keyframes) but make seeking and bitrate switching coarser.
In adaptive streaming, GOP length must align with segment boundaries and be consistent across all renditions, because the player can only switch quality at a keyframe. A closed, aligned GOP structure is what makes seamless ABR switching possible; misaligned GOPs cause stalls or visible glitches at the switch point.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
GOP length trades compression against how cleanly a player can seek and switch renditions, so it must line up with segment boundaries. We wrote seven volumes covering the video stack; for GOP structure start with Volume 1 on frame types, rate control, and encoder settings, then Volume 2 on segment packaging, with ABR switching in Volume 3. Written by Nikolay Sapunov, CEO at Fora Soft.
Choosing GOP length and keyframe spacing for adaptive streaming?
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