@viator42 4k 放大为 1080p 的在此

1080p, 2k, 4k 的显示器都在用，2k 看 1080p 的直播确实比较糊，鄙人也会楼主一样会去看龙神直播，1080p 上开蓝光 15M 非常舒服，2k 显示器上看，明显可以感觉出不如 1080p 的显示器

找到个国外的回答，大家品品

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Short answer: Not really, and you might be better off watching it at 720p

Long answer: Most displays have an aspect ratio of 16:9, and this is what I will assume for this answer.

1080p content is generally 1920x1080, shortened to 1080p. Your monitor is likely 2560x1440 which is bigger than 1920x1080 so it should work, right? Wrong! 1440 is not divisible by 1080! This means that every pixel of the 1080p video will take up 1.333… square pixels. You obviously can’t have a third of a pixel, so the graphics card/monitor has to guess a bit, and you lose a bit of information. The reason 720p works is because 1440/720=2. This means that a 720p video will take up exactly 1/4 of your display. “Well that’s no use at all!” you say, but I counter with my TimesFourInator (patent pending). Since a 720p video would normally take up 1/4 of your screen, you could just expand it so that each pixel of the video takes up 2x2 pixels on your screen. This way, no information is lost and the computer doesn’t have to guess. You’re technically seeing less stuff, but it might look a bit sharper.

What really matters, though, is that you watch your YouTube however you want!

This answer also applies to 4k displays. A 1080p video will take up exactly 1/4 of a 4k display (3840x2160) so it will upscale well, while a 1440p video will not.
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https://www.quora.com/Why-does-1080p-videos-on-YouTube-look-blurry-on-a-27-inch-1440p-monitor-Is-there-a-way-for-YouTube-to-automatically-upscale-the-1080p-video-to-1440p-or-is-there-a-way-to-make-the-video-appear-less-blurry