If you captured every frame in a video as a complete, high-quality image, your video files would be huge – really huge! The Canon EOS 5D IV when took some flak when it was first introduced back in 2016 for using an older MJPEG format that did exactly that.
It also highlights the key difference between what we now call Long GOP compression (smaller files, potentially lower quality) and All-Intra, or All-I compression (larger files, potentially better quality).
