[varelaz]

Codecs are algorithms how to generate B and P frames. I frames are just jpegs. Yes, codecs can split video differently, but in case of the same split the same frame will be encoded the same way. In most cases key frame frequency is just a number. Some formats like HLS cannot work with variable key frame frequency at all. Why it matters, because different version of the same codec can replay the same video differently for B and P (no guarantee), but not I frames. So I frames are the most stable.