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Old 25th July 2020, 19:15   #1  |  Link
YaBoyShredderson
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Transparent encodes of fake 4k blurays

My goals when encoding are to be indistinguishable from the source based on my viewing conditions, with a bit of quality buffer should those viewing conditions change (closer seating, larger tv etc).

I havent started encoding my 4k blurays just yet, only 1080p, as i want to get a ryzen 4000 processor before to speed things up a tad. But i wanted to know if i should downsample them to 1080p?

Obviously true 4k i should leave as is, but with fake 4k, stuff that was mastered at 2k and then upscaled to 4k, should i leave that in the full 4k? Or will it be the same quality at 1080p as thats what it mastered at? I would likely save a whole lot more space doing this.
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Old 27th July 2020, 02:21   #2  |  Link
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>1080p doesn't matter so much with SDR, but absolutely can with HDR so that sharp specular highlights can be preserved.

There isn't always a hard line between fake and real 4K, as titles may combine 4K elements with 2K VFX shots. How much grain and motion blur have a big impact on potential detail as well.
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Old 27th July 2020, 07:25   #3  |  Link
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Also 2k Upscaled UHD Bluray benefit from better chroma resolution. (Near 444 related to 2k)

When downscaling an UHD Bluray with 2k content to 1080p, one will reduce the chroma to a quarter of its original resolution.
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Old 14th August 2020, 23:37   #4  |  Link
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Quote:
Originally Posted by scharfis_brain View Post
Also 2k Upscaled UHD Bluray benefit from better chroma resolution. (Near 444 related to 2k)

When downscaling an UHD Bluray with 2k content to 1080p, one will reduce the chroma to a quarter of its original resolution.
Not necessarily. If someone doesn't care about playback compatibility, when using a reverse upscale filter, the idea would be to reverse upscale the luma inverting the kernel (i.e Debilinear, Debicubic etc) to the original resolution but leaving the chroma as it is, which means that you're gonna end up with a FULL HD 4:4:4 10bit file from an upscaled UHD 4:2:0 10bit which is a win win.
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Old 20th August 2020, 02:22   #5  |  Link
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Not necessarily. If someone doesn't care about playback compatibility, when using a reverse upscale filter, the idea would be to reverse upscale the luma inverting the kernel (i.e Debilinear, Debicubic etc) to the original resolution but leaving the chroma as it is, which means that you're gonna end up with a FULL HD 4:4:4 10bit file from an upscaled UHD 4:2:0 10bit which is a win win.
It would be VERY unusual content for there to be a visible difference between downscaling to 4:4:4 or 4:2:0. Something like very sharp red text on a blue background or something. I don't believe I've seen actual TV/movie content where 4:2:0 at 1080p and above wasn't adequate.

Screen recordings, sure. Turn off ClearType before doing screen recordings, people! It messes up the chroma for people with different types of panels.
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Old 20th August 2020, 07:50   #6  |  Link
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I don't believe I've seen actual TV/movie content where 4:2:0 at 1080p and above wasn't adequate.
Actually I see it all the time, when the content is crisp enough.
It bothers me.
That's why I try to use MadVRs chroma reconstruction/upsampling most of the time I use thr PC to playback movies.

Anyways YUV444 files won't be too compatible with SmartTV or Bluray players. So we are stuck here with 420 chroma.
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Old 24th August 2020, 18:40   #7  |  Link
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Actually I see it all the time, when the content is crisp enough.
It bothers me.
Can you give some examples where you see this?

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That's why I try to use MadVRs chroma reconstruction/upsampling most of the time I use thr PC to playback movies.
Is the problem perhaps in the display pipeline, not the encode? There are obviously different algorithms that could be used for how to optimally go from the 4:2:0 to the display's RGB. Nearest Neighbor is going to be a lot worse even compared to a basic bilinear.

Quote:
Anyways YUV444 files won't be too compatible with SmartTV or Bluray players. So we are stuck here with 420 chroma.
>4:2:0 chroma samples haven't ever been used in a broadly supported distribution format, disc or streaming. 4:4:4 doubles memory buffer and bandwidth requirements, and increases bitrate some, and demonstrated gains have never been worth the extra cost.

Put another way, 1440p 4:2:0 is fewer samples-per-second than 1080p 4:4:4, and will look better for 4K source content.
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Old 29th July 2020, 07:23   #8  |  Link
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Ok, makes sense, leaving at 4k is the best for me then. Thanks.
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Old 1st August 2020, 10:11   #9  |  Link
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Before you make a choice that will hugely impact both encoding time and storage space, just watch a few downsampled to 1080p and then upscaled again to see if you can tell. Some can, many can't, and there's not much point if you can't.
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Old 1st August 2020, 14:09   #10  |  Link
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Before you make a choice that will hugely impact both encoding time and storage space, just watch a few downsampled to 1080p and then upscaled again to see if you can tell. Some can, many can't, and there's not much point if you can't.
This. I use a method that utilizes the clever tool called Zopti to determine optimal (well, at least better than using the same values for all sources) parameters b and c for BicubicResize to downsample. There's a huge difference compared to just using Spline36 or Lanczos. For native 4K, I go for 1440p and upscaled 2K goes down to 1080p.
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Old 7th August 2020, 21:09   #11  |  Link
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scaling down to 1440p might be a good middle ground.
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Old 11th August 2020, 01:13   #12  |  Link
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And note that even "uprezzed" 2K to 4K titles don't use some fire-and-forget algorithim like bicubic. There is a lot of shot- and scene-based tweaking of parameters to get best results. For major titles from major studios, it's more like a lightweight remastering. And if it was a DCI-P3 master getting converted to HDR, it really IS a remaster. What you'd get scaling back down to 1080p isn't going to be the same as the original 2K master (which was 2048x, not 1920x; ~14% more source pixels).

Note a cinema "4K" projector is 4096x, not the home video/broadcast 3840x.
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Old 2nd September 2020, 18:39   #13  |  Link
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It looks like DOTA2 has the most extreme examples of single-pixel transitions between brightly saturated to no chroma, so I'll do some test runs like that.

On an initial test with Witcher 3, CRF 18 still left a lot of visible blocking and banding. The default aq settings aren't well tuned/effective adapting for that sort of material. DOTA2 is quite different, so I'm going to stick with CRF 18 to start.

Bitrates were pretty much identical between 420 and 444, probably because of:
Code:
x265 [warning]: halving the quality when psy-rd is enabled for 444 input. Setting cbQpOffset = 6 and crQpOffset = 6
Which should make apples-to-apples comparisons easier, as the same amount of bits should be allocated to both luma and chroma in either mode. Although any potential gain from 444 might require lower Qps for chroma to retain those edges.

Here's the DOTA2 command line I'm kicking off. These seem reasonable?

Code:
ffmpeg.exe -i DOTA2.mov -pix_fmt yuv420p -f yuv4mpegpipe - | x265.exe - --y4m --preset slower --pools "+,-" --keyint 240 --crf 18 --vbv-maxrate 5000 --vbv-bufsize 15000 -o DOTA2_CRF-18.hevc

ffmpeg.exe -i DOTA2.mov -pix_fmt yuv444p -f yuv4mpegpipe - | x265.exe - --y4m --profile main444-8 --preset slower --keyint 240 --crf 18 --vbv-maxrate 5000 --vbv-bufsize 15000 -o DOTA2_CRF-18-444.hevc
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Old 18th December 2020, 06:44   #14  |  Link
takla
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For bit depth in video games, I recommend to check out this nifty tool. It is developed by Kaldaien. He made it his mission to streamline HDR in PC games, which currently follows basically no standards and is mostly brocken (at least brocken when compared to what can be achieved with this tool properly set up). It can show you what native bit depth and color space a game uses and overwrite it, when supported, with scRGB HDR 16-bit.

And for 4:4:4 chroma talk, personally, I watch a lot of twitch tv streams which I pipe to MPV. It is very obvious to me to tell the difference of 540p to 2160p chroma on my 55" 4k Samsung TV. I use the excellent KrigBilateral glsl shader to get chroma to almost native res. Good examples I recommend to test for chroma are UI heavy games like World of Warcraft and Path of Exile.

And thankfully this samsung tv also supports freesync, which removes all judder in low fps videos once mpv is in exclusive fullscreen (default key is f) this is achieved by the gpu driver telling the display to double its refresh rate when outside freesync range (24>48fps with 48to60hz range)

Last edited by takla; 18th December 2020 at 07:02.
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