[knaik94]

That's optimized based on the video codec itself where you keep frames with major changes but surrounding frames can be optimized by encoding where certain pixels move. That's essentially what the bitrate tells us, how much of the bits are new and how many are copied from a previous frame. This is an oversimplification, but with static images, you would need a low bitrate after the initial few frames because it doesn't change. And bitrate is a proxy to how much data is transmitted while streaming, it's bits per second.

So a more concise answer, the codecs used for video by YouTube have the optimization you're thinking about built in. It would send a "pixel didn't change from last frame" and not need to send all the color information for all the pixels.

YouTube does not really do variable frame rate, and it's messy for editing, but it's another optimization that is possible and could be useful for the type of video you're describing.

The article describes DASH which you would need to send the full frame initially every time segment but per segment the previously described concept still applies. I don't believe YouTube uses DASH for anything outside live streams.