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I watch 4320p (8K) streams when possible because it noticeably improves the quality on my 4K screens — and this is with my worsening eyesight! That shouldn’t b

I watch 4320p (8K) streams when possible because it noticeably improves the quality on my 4K screens — and this is with my worsening eyesight! That shouldn’t be noticeable if the 4K stream was encoded properly.

koromak 3y ago
Similarly, 4K video looks much better on a 1080p screen than a 1080p video. A youtuber posted a comparison, its easy to see even in a still image. Its all in their encoding algorithm.
edvinbesic 3y ago
I believe this is to some degree due to chroma key subsampling, where in a 4k stream you will only have 1080p worth of light intensity encoded (cluster of 4px). So if you play an 8k stream and downscale to 4k you actually have full chroma (1:1). There could of course be other factors involved as well but this is definitely a pretty big contributor.
- olaulaja 3y ago
  You have chroma and luma the wrong way around, chroma is color and luma is light intensity. Chroma is still the thing being subsampled. I've never really noticed effects from chroma subsampling so my guess would be the bitrate just being better with the higher resolution. Also "full res->compress->downsample" might be more efficient than "full res->downsample->compress" since downsampling is a (really bad) form of lossy compression as well.
kevincox 3y ago
> That shouldn’t be noticeable if the 4K stream was encoded properly. I don't think this is true. At some point there are diminishing returns. At some point if the 4k video has twice the bitrate it is going to have more information available. Some will be lost in the down sampling but it isn't "improper" to end up with more data on the screen. It is true that YouTube bitrates are pretty "conservative" for the resolution but I don't think that is "improper" it is just a tradeoff based on common device an internet speeds. They could be more bandwidth efficient if they did a custom transcode for each user's screen size and bandwidth but that is infeasible. So it is fine that some users will not be able to stream the 4k transcode on their 4k screen and will need to use the 2k stream and some users will have extra bandwidth on their 1080p screen so will stream the 2k version for better quality. The goal isn't to be perfect for each device but to be good on average.

koromak 3y ago

Similarly, 4K video looks much better on a 1080p screen than a 1080p video. A youtuber posted a comparison, its easy to see even in a still image. Its all in their encoding algorithm.

edvinbesic 3y ago

I believe this is to some degree due to chroma key subsampling, where in a 4k stream you will only have 1080p worth of light intensity encoded (cluster of 4px). So if you play an 8k stream and downscale to 4k you actually have full chroma (1:1). There could of course be other factors involved as well but this is definitely a pretty big contributor.

olaulaja 3y ago
You have chroma and luma the wrong way around, chroma is color and luma is light intensity. Chroma is still the thing being subsampled. I've never really noticed effects from chroma subsampling so my guess would be the bitrate just being better with the higher resolution. Also "full res->compress->downsample" might be more efficient than "full res->downsample->compress" since downsampling is a (really bad) form of lossy compression as well.

kevincox 3y ago

> That shouldn’t be noticeable if the 4K stream was encoded properly. I don't think this is true. At some point there are diminishing returns. At some point if the 4k video has twice the bitrate it is going to have more information available. Some will be lost in the down sampling but it isn't "improper" to end up with more data on the screen. It is true that YouTube bitrates are pretty "conservative" for the resolution but I don't think that is "improper" it is just a tradeoff based on common device an internet speeds. They could be more bandwidth efficient if they did a custom transcode for each user's screen size and bandwidth but that is infeasible. So it is fine that some users will not be able to stream the 4k transcode on their 4k screen and will need to use the 2k stream and some users will have extra bandwidth on their 1080p screen so will stream the 2k version for better quality. The goal isn't to be perfect for each device but to be good on average.