Playing with "Match Content" and "HDMI output"

[Michelasso]

My 4K HDR Sony Bravia (and the very cheap HDMI cables from Amazon!) supports all possible output formats for SDR and HDR10 (no Dolby Vision on my TV, though). So I played a bit with the settings. I have tvOS 11.2.5 beta. These are the main scenarios:

ATV4K on HDR 50/60Hz 4:2:2 - Match Content disabled:
There are no black screens when starting a video in either SDR or HDR. But the GUI colours are quite washed. I can "fix" it turning the Color up to 70 (default is 50) in the TV settings. It's quite far from my ideal. I didn't check the other options because I see no reason to enable the Match Content if I decide to have the GUI and apps in HDR.

ATV4K on SDR 50/60Hz YCbCr 4:4:4

• With Match Content: Range (for HDR):
  I can watch any SDR video without getting any black screen (caused by the TV changing settings). Obviously I get the temporary black screen with the delay when watching HDR content. I have the feeling the image isn't excellent (it's very slightly washed)
  
• With Match Content: Range & Frequency:
  As above but I get plenty of black screens while switching from an app to a video and vice-versa.

ATV4K on SDR 50/60Hz RBG Low or High:
The image seems better, but I think there is a bit of "crushed black". Especially with RGB Low (which should be the full RGB range if I understood correctly), although they look quite similar to me. The TV always switches when playing a video, no matter the frequency match.

Personally I'd like to keep this last setting, but the TV switching can get annoying with time. Especially watching short video clips. I have actually opened a bug report with Apple, hoping something can be done to fix it. Otherwise, what would anyone suggest? Is it the "switching" from SDR to SDR in RGB mode an issue only with my Bravia or it generally happens with other 4K TVs as well?

 

[priitv8]

Maybe you should play with Gamma (lower to -1 or even -2), not the Saturation, to fix GUI colors in permanent HDR mode?
Another one is the Black Point.
It is the black levels, that get elevated in HDR mode, not the saturation decreased.
You can observe it via the PLUGE bars on the Calibration screen of tvOS settings.

 

[Michelasso]

I have tried to switch few parameters, Gamma included, from an extreme to another, the only one fixing the washed colours was Color indeed.

About the Pluge bars.. Something must be wrong on my TV/display, then. Because I have been unable to get anything like that. It's either any other one lighter (like black-drak grey-black-dark grey) or just black. In either SDR or HDR. But now that I know how it should look like I'll give it another try.

 

[betasp]

I think most TVs have to go to black (and sometimes blink) to switch refresh rates. It happens with my Shield, also. I find it’s less obtrusive on my Apple TV. I think it has to do with how it checks the refresh rate after it switches.

 

[priitv8]

I have tried to switch few parameters, Gamma included, from an extreme to another, the only one fixing the washed colours was Color indeed.

About the Pluge bars.. Something must be wrong on my TV/display, then. Because I have been unable to get anything like that. It's either any other one lighter (like black-drak grey-black-dark grey) or just black. In either SDR or HDR. But now that I know how it should look like I'll give it another try.

Check the backlight!
PS I've just ran the calibration on mine, and as expected, the backlight is turned way on OOB.
In SDR mode I had to dial it down to 5 (!) to achieve 120lm, in HDR mode to 40 (to have about 100lm on a 50% white patch). So you may want to play with that slider as well.

 

[Michelasso]

I think most TVs have to go to black (and sometimes blink) to switch refresh rates. It happens with my Shield, also. I find it’s less obtrusive on my Apple TV. I think it has to do with how it checks the refresh rate after it switches.

Yeah, I figured out something like that as well. Indeed if I use YCbCr I don't turn on the frequency matching. I rather have smooth transitions. I keep it always at 60Hz and that's it. Not that I have ever noticed any difference matching the frequency (unless it is my TV doing the job as it says in the description. Or whatever they mean).

@priitv8 I am checking the pluge bars. I am not sure I understand the description in the image you posted: Both LEFT and CENTER should match the Large Black Bar, and RIGHT should be a little lighter than Large Black Bar.

Which Large Black Bar? Then what does it mean? That Left and Center must be Black and Right must be Dark Grey? In my MBP I get Black-Dark Grey-Grey. In the ATV with SDR I can get Dark Grey-Black-Gray. And those bars are heavily affected by the Gamma indeed. Also by the "Black adjust".

Oh, and yes. I see now that in HDR a lower Gamma does help with the washed colours. And it is usually showing 3 Pluge Bars. Not sure what's going on, unless that's because yesterday I reset the color settings in the TV. It seems to look much better in HDR than when I did my previous tests.

Then let me ask: I was 100% positive that the SDR and HDR settings were different in Android 7.0 in the Bravia. Now I see only the brightness changing switching between SDR and HDR? Hopefully I won't have to factory reset AGAIN that TV!

 

[Scott Davilla]

If you enable frequency matching and your video does not match the current display refresh rate, the AppleTV 4K will always switch the display rate to match. That's what frequency matching means.

All UHD/HDTV's will transition to black when the display rate is changed. Basically your display becomes unhooked while it switches, settles and is reattached. There is nothing you can do to eliminate this transition effect. Some HDTV's switch and settle faster, some are slower. There is a future HDMI spec that aims at improving the switch effect but no one at this time implements it.

 

[priitv8]

@priitv8 I am checking the pluge bars. I am not sure I understand the description in the image you posted: Both LEFT and CENTER should match the Large Black Bar, and RIGHT should be a little lighter than Large Black Bar.

Which Large Black Bar? Then what does it mean? That Left and Center must be Black and Right must be Dark Grey? In my MBP I get Black-Dark Grey-Grey. In the ATV with SDR I can get Dark Grey-Black-Gray. And those bars are heavily affected by the Gamma indeed. Also by the "Black adjust".

Oh, and yes. I see now that in HDR a lower Gamma does help with the washed colours. And it is usually showing 3 Pluge Bars. Not sure what's going on, unless that's because yesterday I reset the color settings in the TV. It seems to look much better in HDR than when I did my previous tests.

Then let me ask: I was 100% positive that the SDR and HDR settings were different in Android 7.0 in the Bravia. Now I see only the brightness changing switching between SDR and HDR? Hopefully I won't have to factory reset AGAIN that TV!

To begin with, these Pluge bars are only good for setting black level in SDR. The meaning of these bars and how to adjust your screen's black level, is explained a bit better here.
In HDR mode, they are indeed all 3 visible.
If you see all 3 bars in SDR, then your black level and/or backlight is too high.
I will have to test it, but while calibrating, I also noticed that the color adjustments are common for SDR and HDR modes.
If that also applies to Contrast, Gamma, Black level and all those fancy black/contrast/FALD adjustments at the very bottom, I need to double-check.
You might want to read Calibration for "Dummies", that one described in quite easy terms what is it all about, the accociated terms and even touches HDR side of the process.

 

[Michelasso]

To begin with, these Pluge bars are only good for setting black level in SDR. The meaning of these bars and how to adjust your screen's black level, is explained a bit better here.

Yeah, I had found that doc myself. So, if I understood it correctly, it says that the Pluge Bars must be "Black-Black-Dark Grey". Which is more or less what I was getting. In any case brightness and contrast do nothing to them. They change only varying Gamma and Black Adjust. Which I have always kept at Medium/High. With Black Adjust OFF it shows 3 bars.

In HDR mode, they are indeed all 3 visible.

Good to know!!! I had a cold vibe when i saw that whatever I did they were always 3 bars. In any case, can this be related to the "fog effect" I see with some HDR content? As if in HDR they use as black the one that turn grey in the bars instead of black. It usually happens with Netflix (I watched Bright last night and the image was horrible).

If you see all 3 bars in SDR, then your black level and/or backlight is too high.
I will have to test it, but while calibrating, I also noticed that the color adjustments are common for SDR and HDR modes.
If that also applies to Contrast, Gamma, Black level and all those fancy black/contrast/FALD adjustments at the very bottom, I need to double-check.
You might want to read Calibration for "Dummies", that one described in quite easy terms what is it all about, the accociated terms and even touches HDR side of the process.

I'll have to test it again myself but I am 99% sure that at least Brightness, Color and Contrast where changing between SDR and HDR. I even wrote a small guide after upgrading to Android 7.0. This with "App (Video)".

Actually I have tested it now with the Android TV Amazon app. It's on "Personal" with the "App (Video)" settings. Switching between SDR and HDR only the brightness changes. Same using "Cinema Home".

I may try to reset the TV to factory settings (AGAIN!). I know the Pictures settings are bugged for sure, because sometime I get the settings for HDMI 2 when using an Android app. I hate the OS of this TV, it's unbelievably broken.

@Scott Davilla Ok about the frequency, that makes sense indeed. But why, when in SDR and watching SDR content the TV needs to switch if I use RBG Low/High instead of YCbCr? I thought that wasn't content dependant, in the sense that I believed that's only how the signal gets transcoded and sent from the ATV to the TV. I mean, I am not really an expert about video decoding.

 

[Scott Davilla]

It all depends on HDMI formats that your UHD/HDTV supports, some refresh rates might not be not available under YCbCr but are under RBG Low/High. The AppleTV 4K gets the display EDID which indicates what it can do. Then AppleTV then builds a list of possible rates that are supported for the HDMI format that you set in tvOS. If the media matches this list, it switches.

 

[Michelasso]

It all depends on HDMI formats that your UHD/HDTV supports, some refresh rates might not be not available under YCbCr but are under RBG Low/High. The AppleTV 4K gets the display EDID which indicates what it can do. Then AppleTV then builds a list of possible rates that are supported for the HDMI format that you set in tvOS. If the media matches this list, it switches.

Yeah, but to avoid/reduce switching I disable the frequency matching. So in SDR 50Hz RGB Low signal it should always output an SDR 50Hz signal. Do the TVs need to match the YCbCr/RGB as well and switch accordingly to get the best setting between YCbCr and RGB?

Also I would be interested to know why Android TV can move seamlessly between SDR and HDR from an app while it needs to switch using the HDMI. Or at least I never noticed and transition. Unless doing it internally (so without dealing with HDMI) it is much faster.

 

[Scott Davilla]

YCbCr/RGB is a user setting. You pick either YCbCr, RGB low or RGB high. Then the Apple TV picks the rates within that range. It does not auto switch between YCbCr, RGB low or RGB high.

If you don't see the display switch, then it's not switching The AppleTV and Android TV can handle SDR/HDR conversions without switching. That's what happens when frequency switching is disabled. SRD/HDR are color ranges, frequency switching handles the display refresh rate.

Optimal playback is when display refresh rate matches the media content frame rate. The issue here is 23.97 frame rate media content does not fit exactly into 50Hz display rate. So frames are dropped to keep audio/video in sync. It's the frame drop prevention that purists are after and what 'frequency switching' is all about.

 

[Michelasso]

@Scott Davilla No, sorry. I don't understand. I do see some switching when in (any) RGB mode with frequency match off. None when using YCbCr. Obviously talking about SDR settings with SDR content.

So what causes it? I mean, it gets quite annoying because for example the Netflix previews play just fine, with right colours (in SDR) and then starting the stream it switches. I mean, I ask more for "academic" purposes. At this point I'll keep YCbCr at 50Hz with the frequency matching off. It isn't much of a compromise to me anyway.

 

[Scott Davilla]

Now you are asking asking App specific details. It could be that Netflix app does not do display switching when doing previews. That would make sense. Why switch for a preview, no one cares about frame drops in a preview.

The range/rate switch API does have the ability to tell tvOS to not switch rate and/or color range. For example, in MrMC we have a setting to enable/disable display rate switching. If tvOS has it enabled, but it is disabled under MrMC, no display rate switch will happen.

The switching API is a request to tvOS. Send the request and if tvOS can switch, tvOS will. It also depends on if Apps are using the native tvOS player or their own internal player. If using native tvOS player, then Apps have the ability to tell tvOS not to switch.

From what I've seen from console logs, Netflix uses the native tvOS player.

Display rate switching is a two headed demon, some people want it as they can't stand frame drops from mismatched display/media frame rates. Others can't stand the display switch effect as everything goes black and playback stops for a few seconds. That is why in MrMC, we let users control it and they can pick which flavor fits their minds and eyes

 

[mattopotamus]

If you enable frequency matching and your video does not match the current display refresh rate, the AppleTV 4K will always switch the display rate to match. That's what frequency matching means.

All UHD/HDTV's will transition to black when the display rate is changed. Basically your display becomes unhooked while it switches, settles and is reattached. There is nothing you can do to eliminate this transition effect. Some HDTV's switch and settle faster, some are slower. There is a future HDMI spec that aims at improving the switch effect but no one at this time implements it.

one of the few benefits to HDMI 2.1 right out of the gate.

 

[Scott Davilla]

More like promises that HDMI 2.1 offers. It remains to be seen how well (or badly) it gets implemented. Some UHD/HDTV makers still have not gotten their EDID reporting correct, even after decades of that ability being present.

And personally, bought a new Samsung UDH/HDTV a year ago. Not about to replace it soon just to get HDMI 2.1.

 

[mattopotamus]

More like promises that HDMI 2.1 offers. It remains to be seen how well (or badly) it gets implemented. Some UHD/HDTV makers still have not gotten their EDID reporting correct, even after decades of that ability being present.

And personally, bought a new Samsung UDH/HDTV a year ago. Not about to replace it soon just to get HDMI 2.1.

Agreed. There is nothing in 2.1 that will make me upgrade my current set. I have a DV capable OLED, so I feel pretty set in that realm for the foreseeable future. HDR10+ doesn't really intrigue me because DV isn't that different than static HDR10 in real world usage.

 

[Michelasso]

@Scott Davilla Thanks for the explanation, informative as usual. Still, don't take me for stupid (just stubborn! ), but I don't get the answer to my question: Ok about the frame rates, I understood it. But I have the frequency matching disabled. So why in RGB, with frequency match OFF, I still get the infamous switching? The frequency is stuck at 50Hz.

As, I thought, the signal in output is fixed to RGB Low or RGB High. They should be the apps/tvOS converting the videos to RGB Low/High. At least that's what I understood. Or the apps, since the Color Range match is ON, can decide to output in either YCbCR or RGB High/Low instead of converting everything in RGB on the fly? What for, in case? My understanding was that an YCbCr signal can always be converted to RGB on the fly.

Again, I am not really an expert on this, I am gradually learning things.

PS: Switching apart, which would be the best colour range for SDR? YCbCr 4:4:4, RGB Low or RGB High?

 

[Scott Davilla]

Opps, forgot that format (YCbCR or RGB High/Low) does not mean a fixed SDR or HDR. Those depend on how the UHD/HDTV works internally I guess. Some must have to do a switch, some don't.

Personally, I stick with YCbCr. Less choices to confuse me My motto, if it looks good and no one is complaining, ship it. LOL. But seriously, video media content is YCbCr, so let's try to keep the number of color space conversions that happen when picture frames propagate from the decoder, to renderer, and out to the UHD/HDTV.

 

[Michelasso]

@Scott Davilla Well, yeah. As I wrote I decided to stick with YCbCr myself. At the end the RGB modes somehow looked a bit darker to me.

Anyway, I have finally seen the benefit of frequency matching! In a episode of "Hatfield &McCoy" in Netflix the camera was panning over some thumb stones. And the letters were "vibrating". So I enabled the frequency matching, I had already the "Motionflow" (the frame interpolation, whatever is called) set to "Normal", which is medium and the video in that point was smoother. Although now I am not sure if it has been the 24fps signal doing it or the combination of it and the Motionflow. Too bad that with Motionflow enabled I get the soap opera effect, so I went back to my regular settings: 4K SDR 50Hz/YCbCr 4:4:4/Only range matching enabled (for the HDR). And there it stays. The switchings drive me banana!!!