The default is 72 which is in frames I suppose. However what happens if I simply uncheck it? Does it work like AVC Intra where key frames doesnt exist and every pixel in every frame is processed like in MJPEG?
AVC intra and MJPEG are intra frame (keyframe) encoding only, each frame in your video will be encoded as a whole. Distance between key frames is a parameter for inter frame compression, where some pictures are encoded either as a whole (i-frames a.k.a. keyframes), and pictures between keyframes are encoded in reference to other frames either before (p-frames), or before & after (b-frames). If you uncheck custom distance between key frames, you essentially tell your encoder that you don’t care about it, and it will chose to add a key frame whenever it needs to, mostly depending on the amount of motion in the scene, and encoder implementation details. The more keyframes in your encoded video, the heavier the average bitrate / file size. AVC intra is actually based on h264, but uses only keyframes, and no inter frame compression. MJPEG is basically a sequence of jpeg muxed in a video container.