Key frames are like compression markers, they instruct the codec to start the calculation of how to create a frame, from scratch. A key frame, otherwise known as an I-Frame is the starting point for all frames proceeding that frame until the next I-frame. (I'll not complicate this explanation with B and P frames).
Every piece of video starts with an I-Frame
Modern codecs set keyframes automatically based on their own internal calculations as to how different one frame is from the previous frame.
You are referring to how to manually force keyframes to be inserted and the general, basic rule is to set this to be 10x the frame rate (for standard def material). So if your target frame rate is 25fps, then your keyframe setting would be every 250 frames or every 10 seconds.
Your setting is correct.
[Blake Porter]"When people try to scroll back in the video, the video still needs to pre-load... "
That's nothing to do with keyframes but rather to do with how the video is buffering or has buffered.
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