[Tarkus_]

10Bit HEVC is working fine.

I was just also struggling with not working playback fo the last days and it seems that the problem is HDR when your TV is only SDR.

Plugged it into the an LG CX everything is fine. Back in my Sony KD-X9005A (1. gen 4k w/o HDR) it does not work with HDR content. First thought of the default audio layer problem but then I remembered it worked ony my CX when I got it. So I cross checked.

Any known option for proper HDR>SDR conversion?

I had no time to pack the debug informations yet as Christmas is coming, but I hope can do it in some days. BUT! What @myblade wrote could be the exact problem at least my problem. As I wrote in my original post my current TV is just one more years old SAMSUNG - 55D7000 what is not only not HDR capable but not 4k. You could ask me then why I care about 10bit 4k HEVC, but in the near future I would like to change my TV so I'm trying to getting ready for it. Anyway. The problem is problem.

My TV is 'also' HDR incapable so this could be really the reason of the overloaded Kodi. 8bit 4k HEVC is totally fine for me while my TV is just 1080p. 10bit sadly not. But as I wrote, through remote casting the same video there is no problem with that. The only difference the 2 situation is the decoder itself. With casting the video decoder is the GCGTV own process handler while when playing with Kodi that could be Kodi's own. For me seems that with 10bit videos on 8bit TV Kodi not use hardware decoding and 10bit 4k without dedicated multimedia processing is really 'resource hogger'. I don't know why could this happens but seems for me this is the problem. 8but 4k rendering seems HW decoding as the result is almost fine, and only processing through SW should be resulting stuttered.

@fritsch what is your opinion? @myblade situation seems exactly what I found. Could be any possible fix for it? Or wait further for my debug logs?

I think you're probably on to something.  On my 4K Firestick, I struggled playing 4K videos on my non-4K TV, prior to upgrading.  They'd play, but they'd be really sluggish.  Since upgrading to a 4K TV, they play just fine on the same Firestick.  I have no experience with HDR (my TV doesn't support it), but it would make sense that it could have similar issues.