Do you mean powered off or on standby?
It sounds like an EDID-reading issue. If you start vero with no display connected, it may not be getting the HDR capabilities from the display.
I meant powered off.
But, yes, I just tested it, and it does only revert to 8-bit HDR if the AVR is on standby when it is powered on.
Another mystery solved 
Is it necessary to keep the Vero running in 1080 to ensure the 8bit/10bit colour switching for HDR happens correctly?
I changed the video settings to 2160p, and HDR switching was fine. However the Vero will upscale any 2K video to 4K.
[Edit]
Just to add at 1080p video settings, 4K videos are output correctly at 4K.
[Edit 2]
Actually I only have 10-bit HDR files, and SDR files.
Could you grab debug logs for that situation, please?
Sure:
https://paste.osmc.tv/suqecuhozi
I enabled logging.
Powered off the Vero.
Put the AVR in standby.
Powered on the Vero.
Brought the AVR out of standby.
Played a HDR video, and could see posterization in flatish areas.
You could try doing this after booting with the AVR on
That did not work for me.
I can see the disp_cap file under the /home/osmc/.kodi folder, and I can see that it does appear to list all the display modes my TV supports.
However HDR will still be played at 8-bit.
One other thing I noticed is that, in that situation where the AVR is on standby, and the Vero powered on, the gui resolution drops to 720p. And, a subsequent reboot does not resolve this (although HDR video playback is corrected). So I have to manually adjust the resolution again.
Please post a debug log when this happens
Cheers
Sam
I can see whatās happening in the log already posted, but donāt know if thatās before/after producing the disp_cap file. There is no EDID available at boot, and the device is falling back to 720p, RGB. When an EDID does become available, Kodi doesnāt get to know about it.
Iām surprised this is happening with a relatively new Denon. They should report some basic functionality even when turned off as I understand it.
[Edit for clarification]
Ok.
The original logs are before disp_cap was copied.
These are after:
https://paste.osmc.tv/payahivehe
So the disp_cap file in .kodi makes no difference.
An additional reboot, while the AVR is on fixes HDR playback, but the interface gui is stuck at 720p, unless I manually change it.
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Maybe this only happens if HDMI passthrough is enabled? In my case itās disabled because I connect my SAT receiver direct to the TV.
If HDMI passthrough is enabled (on the AVR, I assume) then the AVR may not be offering any EDID configuration or would only offer the EDID of the TV. If itās disabled, I would expect the AVR to offer some EDID.
13:20:26.238 T:4075360848 ERROR: GetString: error reading /home/osmc/.kodi/userdata/disp_cap
Kodi is struggling to read it - can you post ls -l ~/.kodi/userdata please?
And cat ~/.kodi/userdata/disp_cap.
Edit: Aha! the original instructions are wrong. Should have been:
cp /sys/class/amhdmitx/amhdmitx0/disp_cap /home/osmc/.kodi/userdata/disp_cap
Thanks, thatās pretty much resolved all my issues
However, I canāt help being a bit curious about the AVR EDIT (admittedly itās not a term I had any familiarity with until now):
On the PS4 Pro, with all the video settings set to auto (Resolution, RGB Range, HDR, and Deep Color Output), I do not get any issues when starting it up with the AVR still in standby. When the AVR is started the TV will report resolution of 2160p on the login screen, and HDR games all work fine.
What are your thoughts on this ? I appreciate it might simply be a case of different hardware capabilities, or available libraries.
Just curious; Iām more than happy with how the Vero is working.
EDID is how a display and/or amp tells a source what resolutions, audio formats, etc it can handle. The thing seems to be that Kodi only asks for it once when it starts up. If your AVR and/or TV are not on when you power on vero (or the hdmi cable is unplugged) Kodi defaults to something simple (1280x720 IIRC). If my AVR is on (standby), but not my TV, the AVR indicates a short list of resolutions, including 1080p, so that Kodi is happy when it starts. It looks like your AVR is not even doing that. Donāt know why - maybe some setting you can play with there on the AVR. @Chillbo knows about Denons. The disp_cap file is a hack to give Kodi something to work with if it canāt get an EDID.
Your PS4 probably has a method of sensing a change on the hdmi cable, re-reading the EDID and setting itself to the native resolution of the display as soon as it can āseeā it. Iām now looking at how we could get Kodi to do that.
Thanks for the comprehensive explanation !
