Dark HDR Videos - Non HDR are perfect


Congratulations on the recent update to 4.9 / 19.1. I’ve updated 2 x 4K+ without a hitch.

My HDR files appear unusually dark (Non HDR are perfect), especially in sections of the screen where brightness is low. This characteristic existed prior to recent update, however I didn’t really investigate bc i thought it might be resolved by the updated video stack etc.

Here is my config / observations

  • My 4K+ is set to 1920x1080p @ 60Hz
  • TV Model is Samsung QA55Q6FNA (running latest software) which supports HDR and has a setting for HDR+ Mode (HDR+ selection really dims UI so i turn it off).
  • ISS_4K_HDR10plus_ff.mp4 - too dark in low areas of brightness
  • jellyfish-250-mbps-4k-uhd-hevc-10bit.mkv - hard to tell as background is totally black
  • TV does offer HDR options when playing files which aren’t offered with non-HDR files.

logs - https://paste.osmc.tv/gixexocadu

here is output of: cat /sys/devices/virtual/amhdmitx/amhdmitx0/disp_cap

Cheers, Geoff

This is correct, but you would need to enable adjust refresh rate switching to allow 4k and HDR/HDR+ (see below)

We recommend people with 4K TV’s set their user interface (UI) to 1080p. Kodi’s UI is not optimized for 4K yet and this can put unnecessary demands on your device and can lead to a suboptimal picture quality, as well as potentially cause other issues.

The settings we recommend are as follows…

Settings>System>Display>Resolution> 1920x1080p
Settings>System>Display>Whitelist> (empty) *
Settings>Player>Videos>Adjust display refresh rate> On start/stop

Some televisions may also need, or benefit from, the following being set…

System>Display>Force 4:2:2 colour subsampling> (enable)

With the above settings your UI will be output in Full HD and your 4K content will be output in 4K. *Information regarding the whitelist can be found here. If you have any doubt, feel free to upload some logs so we can verify that your settings are indeed correct.

Just a comment: those jellyfish samples are not HDR afaict. Does your TV think they are HDR?

Not quite right - you need refresh rate switching to get 4k resolution but HDR and HDR10+ (note ‘HDR+’ doesn’t seem to relate to HDR10+) should be available even at 1080p.

From what @geoff_noob says it seems the answer lies in the TV settings, not Vero settings. I would suggest re-setting everything to defaults for the HDMI input port he is using and go from there.

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Although, if you downscale 4K HDR to 1080p you get very obvious 10-bit → 8-bit posterisation/banding in the end result. I don’t know if that’s what OP is seeing, but it’s certainly not going to help the picture quality.

I’ve never seen that and there’s no reason for it (1080p is still 10-bits if the display supports it) and certainly no reason it would make the picture darker.

The output signal is still nominally 10-bit but the posterisation is unmistakeable - run the “World in HDR” clip and you’ll probably see what I mean. Maybe the downscaling is only done at 8-bit accuracy?

Anyway, I’ll take your word for it that this can’t be causing darkening, so we can leave this for another thread! :slightly_smiling_face:

We’ve run this clip especially often for testing… With this and others there’s visibly less banding with 10bit than with 8bit playback on 10bit-capable 1080p panels we’ve tested with. I can definitely not concur with this. There has to be something else at play, if you see more banding than with actual 4K 10bit output.

But back on topic here. :wink: