Why does the quality of a video deteriorate when confetti or snow falls?
If you watch a YouTube video with confetti or snow falling, the image quality can suddenly drop. This is due to the compression and decompression of video data, but YouTuber Tom Scott explains what is happening specifically.
In the days of analog television, video was not compressed; instead, each TV set received the signal sent through the air and displayed it as is. This video was in its original resolution, meaning that you could see almost every bit of what the camera captured.
The above method was fine when there were only a few TV channels, but as the number of channels increases, problems begin to occur. Also, sending the signal as it is is a waste in the first place. The technology that solved this problem is compression.
According to Scott, to transmit every pixel of an HD video in perfect quality without compression, it would take about 1.1 gigabits per second, which is roughly the same as 100 broadband connections used by the average American. For YouTube to work, it needs to reduce that amount of data, or bitrate.
The first step in reduction is image compression. Basic image compression works by throwing away bits that are unnoticeable to the human eye. Using this, we can take every single frame of video and apply the same compression to it.
Step 2 is inter-frame compression. When there is similar data between frames, for example when a scene with a person against a plain background continues for a while, there is no need to transmit the same data (plain background) every time. In this case, the amount of data can be compressed by only handling the difference between the frames before and after.
These two steps have made it possible to view high-quality images even on smartphones.
However, as soon as snow or confetti falls onto the screen, it falls apart.
Scott capped the video's bitrate, which means it limited the number of 1s and 0s per second that were encoded.
Limiting it to 200 kilobits per second makes Scott's image look choppy, but you can still get a sense of what's going on.
Adding snow to this scene makes all the difference. Bits of footage that were only used to draw Scott are now also used to track the snow that suddenly appears. The movement of the snow is chaotic and complex.
Add in confetti and the footage becomes choppy. The more movement there is in a video frame, the greater the difference between frames becomes, until there are no more available bits and the footage falls apart.
Reverting the bitrate limit still doesn't fix it.
However, if you stop everything moving in the air, the image will be played back in high quality after a few seconds.
'The confetti isn't the problem; it's the movement that's the problem,' Scott said. 'That's why when a sports team wins and the confetti starts flying, the image quality goes down.'
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