On youtube, on a 1080p display, 4K video is much better than the same video at 1080p. This is because youtube uses a different, higher quality set of codec sett

On youtube, on a 1080p display, 4K video is much better than the same video at 1080p. This is because youtube uses a different, higher quality set of codec settings and encodes video at a higher bitrate. In a less imperfect world, if you're watching video on a 1080p display, watching a video that is encoded at 1080p will give you the best quality for any given bitrate in any given codec. Ideally youtube would give three setting choices: codec, (ie, if your device supports decoding VP9 in hardware, it will do that, and fall back to successively worse codecs) resolution, and high quality vs low bandwidth. But that would mean 1) encoding every video twice as many times and using about twice as much total storage. I can understand why they've combined these two separate tunable settings into one resolution+quality knob. They do separate out codec though; afaik most videos will be available in VP9, h265, and h264. Possibly others.