A keyframe (an IDR frame in H.264/HEVC terms) is a frame encoded with no dependency on any other frame, so a decoder can begin decoding from it cold. Every GOP starts with one. Keyframes are the only points where playback can start, seek, or switch renditions.
Their placement is a balancing act. Frequent keyframes make seeking and ABR switching responsive and segments cleanly splittable, but they cost bitrate because they cannot be compressed against neighbours. For adaptive streaming, keyframes must be aligned across renditions at segment boundaries so the player can switch quality invisibly.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
Keyframes are the only points where a player can start, seek, or switch renditions, so their spacing must match segment boundaries across the whole ladder. We wrote seven volumes covering the video stack; for keyframes start with Volume 1 on IDR frames, GOP structure, and rate control, then Volume 2 on segmenting, with ABR switching in Volume 3. Written by Nikolay Sapunov, CEO at Fora Soft.
Seeking and quality switches feel jumpy because keyframes are misaligned?
We will check your encoder and packager settings and send keyframe settings aligned across all renditions. 250+ video products shipped since 2005.
