Media encoding includes various forms of compression. Media with more variation and specific detail needs more data to describe it. A simple (but reductive) example is a video file that just shows one frame for 30 seconds. You don’t need 30 seconds of frames (1800 at 60fps) to describe that video, you need one frame, the one you want to see, and some instruction that says “don’t change this frame for 30 seconds”.
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