Can you upload a small sample so I can reproduce the issue?
Do you have an HDR display?
Hi, yes Iāll provide that tomorrow, itās time for bed now. Yes Iāve got a LG oled55b6 and I can play one clip fine in hdr 2160p60 and the TV says itās HDR, but another clip in 2160p24 is just a mess.
Iāll fix some pictures, clips and logs tomorrow. Thanks
Thanks ā looking forward to the sample. The results have been mainly positive so itās important we try and resolve any corner cases.
Hi, hereās some info for you:
Thereās my full log I think. I put the files on an USB3-stick to make sure itās not network related.
At 11:42 I started playing the first clip (demo-uhd3d.com - Ce site web est Ć vendre ! - Ressources et information concernant demo uhd3d Resources and Information.) which plays fine.
Stream #0:0: Video: hevc (Main 10), yuv420p10le(tv, bt2020nc/bt2020/smpte2084), 3840x2160 [SAR 1:1 DAR 16:9], 59.94 fps, 59.94 tbr, 1k tbn, 59.94 tbc (default)
At 11:43 I start the next clip (http://files.hdrsamples.com/downloads/hdr/Exodus_UHD_HDR_Exodus_draft.mp4)
Stream #0:0(und): Video: hevc (Main 10) (hev1 / 0x31766568), yuv420p10le(tv, bt2020nc/bt2020/smpte2084), 3840x2160 [SAR 1:1 DAR 16:9], 42805 kb/s, 24 fps, 24 tbr, 24k tbn, 23.98 tbc (default)
which has some weird red/green flickering in colors going on, and cuts out after ~10 seconds. I get a flash of video/audio and then it goes black and input is lost. Stopping the movie brings me back to kodi.
I hope this helps, let me know if thereās anything I should test.
(worth noting, the video would play ok before this update)
Try another hdmi cable
If you have an AV receiver, use an hdmi 2.0a certified cable between the receiver and the TV too.
The drive strength can be lower than expected on the HDMI PHY, so you need very good cables. This will change in the future.
I will try the clips soon
I just tried with another cable but no difference, although itās just some generic one. The one Iāve been using is the only supplied with the unit. Iāve got the Vero4k hooked up directly to the TV.
Okay ā I will see if I can replicate soon. Thatās why we are still calling this experimental 
I went and bought a new āexpensiveā hdmi certified 21gbit whatnot cable, but no difference.
Edit: I tried running the clips directly on the tv via usb and that worked fine, no color flickering or cutouts.
Edit2: It seems to work better if I donāt change display to playback, running 24hz seems to give more problems than 59/60
Okay ā thatās interesting to know.
Can you paste a debug log w/ 24Hz and one without Adjust Refresh Rate enabled? Itās possible the resolution change means the TV (or we) are gettting confused.
Sam
Yeah sure Iāll get some more logs in a little while. Meanwhile, I tried reinstalling OSMC and once again videos played like normal. Thereās still some color issues though but the videos donāt go to black or anything. (works with both sample files I posted above). I tried filming the color issue with my phone (https://goo.gl/photos/NpTcdQnh11rxzZcH7) but itās perhaps a bit hard to see, but in the grey areas to the right you can kinda see some shimmering. Itās easier to spot while paused but still visible while watching a video as well.
When running the file directly on my TV I canāt see this issues so I think thereās some signal issue.
Iām gonna try reinstall the experimental build now again and see if thereās any changes.
10:15:10 is with and 10:18:01 is without adjust refresh rate.
Without adjust refresh thereās still the color issue, but the full clips plays.
With adjust it clips out after ~10 seconds (before you see the girl+christian bale)
edit: I might be on to something-
After some more testing we have found that none of the LG TVs support chroma 4:4:4 when in a HDR picture mode, regardless of the input icon. This can be seen here . from LG B6 OLED Review (OLED55B6P, OLED65B6P) - RTINGS.com
It seems 4:4:4 is possible if I change my input icon to āPCā which disables several movie settings, but apparently itās a no-go for HDR 
edit2: if I comment out the attr in rc.local I can play files normal again, but with flickering HDR material (moreso at 24fps than 60). I uploaded a small video where I first play a clip from Arrival via USB on TV (hdr) and then switch over to the vero4k box https://www.youtube.com/watch?v=1nihFOKFBdQ , itās hard to capture but I think you can see the flickering in the sky. If I turn off the adjust refresh thereās less flickering but itās still there.
Not quite sure what to do at this point, seems thereās some issue with this configuration and the TV. Is there a way to force 4:2:0 10bit? (I tried changing the rc.local to that but everything went greenāish so not very useful)
edit3: 
When I didnāt have adjust refresh rate the file would actually play at 1080p60hz (since I had Kodi at 1080p) VIC:16 in UI and VIC:93 in movie.
If I change the UI to 2160p60 it seems to work fine (perhaps some color banding in skies) but disp_mode reports VIC:353.
So uh, if I use 2160p60hz in Kodi, and I set my attr to 420,12bit, everything seems to work. This means kodi upscales 1080 material to 4k and the tv does some 2:3 pull-down magic if Iām not wrong. So this seems to work but is it right? Feels like somethingās off 
Hi,
Your edits are very detailed. I checked this when I woke up and had some questions to ask, but after finishing the day and planning to get back this I see that youāve answered some already.
Iāll follow up on this shortly (when less tired)
Thank you for the verbose report
Sam
Hi
No worries, have a look when you get a chance.
It still not good right now. After watching some stuff it seems the TV wonāt accept the signal at random (420,10bit @ 4k60hz), and running hdr material can just end up in garbled lines all over the screen. I donāt know what the problem is at this point tbh. The TV wonāt accept 4:4:4 unless in PC mode (which limits all movie options) and it wonāt accept 4:4:4 in HDR at all. This seems to be a known issue and affects all LG (oled?) tvs. If I force 4:2:0 it kinda works, but HDR is still hit/miss and sometimes it just cuts to black. This also forces me to run Kodi at 4k60 and canāt enable āadjust refresh rateā.
Iām gonna try reinstall the regular build and see how well that one works. What are the main differences with this experimental build?
Would be nice to have someone else with a LG tv confirm if possible 
Edit: I just now realized that the TV can actually play most files from the NAS via DLNA, and I can successfully play all these HDR10 4k files without issues. I also noticed that DTS-MA 7.1 now gets correctly passed through (as DTS) (via kodi it would show as 5.1 but not DTS). With the freshly installed OSMC all files worked normally, but itās 8bit I believe (thereās flickering/banding in skies like that video I uploaded) but thereās no crashing/losing signal at least.
Perhaps Iāll use the Vero as a 1080p/4k (non-hdr) player and use the TV for HDR content. This will also let me use DTS-HD (my amp supports it but itās only hdmi 2.0 so canāt send 10bit/hdr to the TV).
Are there any more options for the amhdmitx device that I can fiddle with? With the current release I tried forcing RBG but that didnāt make anything better.
Edit2: Running the experimental build via my amp (Yamaha RX-V475) I can now play 10bit HDR content! I have to keep the attr as 444,8bit though, since my amp doesnāt do 10bit/hdr. With the regular june version all hdr content would just get gray/washed up, but now they play like normal movies. So I guess for now the Vero will do all my 1080p/4k and the built in TV player will play 4k HDR material.
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If you enable Sync Playback to Display, youād get away with this
For now it seems that there are issues when changing mode. I think the process of changing the mode is racy.
Yes, dithering will be improved. Iām glad to hear this.
Tested the fix today, tooā¦ I had issues playing Billy Lynnās Long Halftime Walk in the 2160p60 HDR version. I couldnāt find a 1080p60 version in SDR (I only own a 1080p TV), so I had to stick to this one.
The dithering (false coloring) is gone now!
But I noticed that VQ is constantly running low to 0% about once every minute resulting in massive skips. But this isnāt a dithering/HDR issue, I guess. @sam_nazarko, how and where should this be adressed? Is this issue already known to you?
Itās not.
Are you playing via SMB still? If so ā can you try fstab based mount. It may just be that you are playing higher bitrate content than normal and didnāt notice this before.
Since the 1080p skipping issue Iāve stayed with fstab mountingā¦
Could be similar to some buffering issues @f0o is also experiencing with high bitrate content. Itās being looked in to, but likely wonāt be related to the changes made available in this thread. Iām glad that colours look better now.
Sam
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But what I can confirm already: the dark color startup bug that has been reported and not fixed yet, seems to have gone with this test kernel.
Just to make sure, I did as advised (after that the bug was gone for me after every reboot):
wget "https://www.dropbox.com/s/jjt87mtlyxic3l1/vero364-image-3.14.29-25-osmc.deb?dl=1" -O vero3-image.deb
wget "https://www.dropbox.com/s/bpyaqkr3azx5nsc/vero3-mediacenter-osmc.deb?dl=1" -O vero3-mediacenter-osmc.deb
sudo dpkg -i vero3-image.deb
sudo dpkg -i vero3-mediacenter-osmc.deb
sudo reboot
sudo chown osmc:osmc /sys/class/amhdmitx/amhdmitx0/frac_rate_policy
I thought in PM the other day you said it was still not fixed? I had assumed you had tried the testing kernel: the issue isnāt fixed in the current stable kernel
Sam