AppleTV 4K keeps dropping to YCbCr 4:2:0 each time it is turned on/switched to

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Level 1

8 points

AppleTV 4K keeps dropping to YCbCr 4:2:0 each time it is turned on/switched to

I'm having an issue with AppleTV 4K last gen, that is connected to non-HDR 4K tv - Panasonic TX-50CX700E.

Whenever I switch on the AppleTV, it reverts back to YCbCr 4:2:0 despite setting it to RGB (high). My tv is calibrated to RGB and copes well with any RGB format for any other device, eg. Playstation 5, PC.

Because of reverting to lowest possible display format, all the apps and all the content is forcing TV to switch to proper RGB 8bit full format, which causes few seconds of display outage. This is so annoying for any streaming TV apps like Youtube as the display format is switched not on app launch but on content launch, so every playback and going back to menu is doing screen switching.

I'm able to set RGB (high) in settings, then the issue is gone, but the settings are saved only until AppleTV powercycle or switching HDMI input on the tv. So basically - this is "per session" setting.

Is there any soultion to that? This seems to be a bug in HDMI subsystem in AppleTV. I have found only one post about this, also I have filled bug report to Apple but it seems it is only a "suggesstion" to Apple and not taken seriously.

Apple TV 4K, tvOS 17

Posted on Sep 3, 2024 3:08 AM

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Answer 1

Sep 3, 2024 4:01 AM in response to tomeq

I'm having an issue with AppleTV 4K last gen, that is connected to non-HDR 4K tv - Panasonic TX-50CX700E.

That appears to be a 2015 TV, with 3× HDMI-in, all of the HDMI 2.0 type, as far as I can tell.

The TV HDMI ports may need to be configured for the connected equipment. I think each HDMI port can be set to Mode 1 or Mode 2. See your TV manual. I think Mode 2 allows for the full HDMI 2.0 bandwidth (18 Gbps, 14.4 data), which may be needed for RGB (or YCbCr 4:4:4) at 4K 60Hz SDR, instead on only 10.2 (8.16) Gbps for HDMI 1.x compatibility.

I think Apple TV may have “throttled down” to 4:2:0 to give you the best for 4K 60Hz SDR with the given HDMI setting on the TV, as 4:2:0 uses half the bandwidth of 4:4:4.

My tv is calibrated to RGB and copes well with any RGB format for any other device, eg. Playstation 5, PC.

All digital TVs can take YCbCr input. All digital streaming content is YCbCr 4:2:0 in nature. The RGB conversion in the Apple TV doesn’t bring a higher quality than what the TV does internally. The only reason for RGB that I see is using a TV as PC monitor, for use different than movie watching.

The noted display outage is more likely for changes in frame rate (or dynamic range, but that doesn’t apply to your SDR TV). If you turn off Apple TV’s Match Content settings, then it shouldn’t go black for a second or so.

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Answer 2

tomeq Author

Level 1

8 points

Sep 3, 2024 9:59 AM in response to Urquhart1244

Hi,

Yes, all HDMIs are set to Mode 2, and as I wrote before - all different inputs can cope with full RGB range at 8 bit without any fallback, this is all ok and fine. Also, YCbCr 4:4:4 works like a charm on each device. AppleTV can do those modes too, but will keep dropping down to YCbCr every time it is turned on or the input/output (depending on which side we look at) being reset. So I need to go to the settings, set RGB full, confirm and I can watch all as I wanted, until power cycle for any reason.

And yes, match content is deliberately turned on - this is causing content to bump mode up to RGB full. When match content is off, it will stay at YCbCr 4:2:0 all the time, in the menus and in the content. And ofcourse, other way around ;) when set in settings to stay at RGB full range, it will stay at full range. Until reset or power on.

I use TV as PC display, which I have calibrated to match my needs :) so RGB full is the only reasonable option.

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Answer 3

Sep 3, 2024 10:14 AM in response to tomeq

Could it be that your HDMI cable isn’t rated for 18 Gbps (“Premium High Speed”) or more? Older HDMI cables may be made for ‘only’ 10 Gbps, and wouldn’t be able use all that HDMI 2.0 is able to push through its ports.

HDMI cable overview - HDMI.org

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Answer 4

tomeq Author

Level 1

8 points

Sep 3, 2024 10:30 AM in response to Urquhart1244

No, cables are even 8K rated. Let me repeat again - AppleTV in this setup can do 4K RGB full, can do YCbCr 4:4:4, as well as any other devices connected to this TV. The only thing which works wrong is that it can't save/remeber the setting and always drop to YCbCr 4:2:0 after each powercycle or input reset. Whenever I bump it up again to RGB, it works. Whenever something (eg. content type - match content) bump it up, it bumps to RGB. BUT this causes screen outage for at least 5 seconds on my tv.

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Answer 5

tomeq Author

Level 1

8 points

Sep 25, 2024 8:06 AM in response to tomeq

Just to dig it out and confirm - after putting hardware EDID emulator in between Apple TV and TV itself, setting hardcoded EDID to YCbCr 4:4:4 at full 4K, 18 Gbps, HDMI 2.0 mode - Apple TV stays at the desired settings between powercycles.

Not a single change in TV settings, cables, anything. Just put EDID emulator box inbetween.

Definitely, Apple TV is the only device that can't properly talk (negotiate proper display values) with the TV mentioned, but why? Even small and cheap Google TV 4K can work easily without anything forced like EDID emulation....

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