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I've heard before that watching 4K video on a 1080p display is still better than watching the same video in 1080p - is that because there's a kind of supersampl

I've heard before that watching 4K video on a 1080p display is still better than watching the same video in 1080p - is that because there's a kind of supersampling going on there?

s_gourichon 5y ago
Generally not the point. Depending on your video player you might only get aliasing artifacts (and virtually always higher resource consumption). The point of selecting a higher definition video stream can be to circumvent bandwidth limitation, if the platform happens to compress too much what it sends by default.
- gallerdude 5y ago
  I thought I heard it applied even with proportionally equal bitrate, but that could be incorrect.
Const-me 5y ago
I think if you watch that 4k video with nearest neighbor downsampling (i.e. the player which drops 75% of pixels and only render 25% of them, one from each 2x2 quad), you’ll get worse quality. Fortunately, that’s not how video players normally resize the videos they play. At the very least, players are using bilinear sampling. For the exact 50% downsampling of 4k into 1080p, this means the GPU averages 2x2 quad of the source video texture into one output pixel. This averaging step hides substantial amount of codec artifacts. That bilinear sampling is even borderline free on GPUs: they have tons of VRAM bandwidth, and texture samplers are dedicated fixed-function pieces of hardware. If you’re using Windows and Media Player Classic, the player has a preference to switch resizing algorithm, Options, Playback, Output, “Resizer” combobox.
nwallin 5y ago
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.

I've heard before that watching 4K video on a 1080p display is still better than watching the same video in 1080p - is that because there's a kind of supersampling going on there?

s_gourichon 5y ago

Generally not the point. Depending on your video player you might only get aliasing artifacts (and virtually always higher resource consumption). The point of selecting a higher definition video stream can be to circumvent bandwidth limitation, if the platform happens to compress too much what it sends by default.

gallerdude 5y ago
I thought I heard it applied even with proportionally equal bitrate, but that could be incorrect.

Const-me 5y ago

I think if you watch that 4k video with nearest neighbor downsampling (i.e. the player which drops 75% of pixels and only render 25% of them, one from each 2x2 quad), you’ll get worse quality. Fortunately, that’s not how video players normally resize the videos they play. At the very least, players are using bilinear sampling. For the exact 50% downsampling of 4k into 1080p, this means the GPU averages 2x2 quad of the source video texture into one output pixel. This averaging step hides substantial amount of codec artifacts. That bilinear sampling is even borderline free on GPUs: they have tons of VRAM bandwidth, and texture samplers are dedicated fixed-function pieces of hardware. If you’re using Windows and Media Player Classic, the player has a preference to switch resizing algorithm, Options, Playback, Output, “Resizer” combobox.

nwallin 5y ago

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.