If a video is a series of numbers, you can take 'averages' of those sequences. However imagine that you don't get all the numbers, you may get wrong numbers or complete garbage. This is the computer responding to that by repeating the last known set of averages as it scans down the page
If you look closely the background isn't perfectly reproduced. It's just hard to tell
No, this is a compression artifact.
If a video is a series of numbers, you can take 'averages' of those sequences. However imagine that you don't get all the numbers, you may get wrong numbers or complete garbage. This is the computer responding to that by repeating the last known set of averages as it scans down the page
If you look closely the background isn't perfectly reproduced. It's just hard to tell