[noggin]

I know there is a lot of concentration on HDR10 ST.2084 PQ HDR support (as used on UHD Blu-ray), but there is now also HLG HDR content appearing in the wild. The BBC are using HLG for UHD on their iPlayer catch-up/streaming platform in the UK.  It is likely to be popular with broadcasters as it is backwards compatible with SDR within the same colour gamut, and has fewer issues around tone mapping than PQ HDR.  (It is also scene referred not display referred - so doesn't need any additional metadata other than 'I'm HLG')

The HLG EOTF is backwards compatible with an SDR EOTF to a reasonable degree, and so doesn't need tone mapping for SDR output in the same way that HDR10 in a ST.2084 EOTF does. When you play HLG stuff in Kodi it's watchable  on an HDR or SDR display in SDR mode if it is output in the correct colour gamut - usually Rec 2020 (not Rec 709), but as Kodi doesn't flag HLG over HDMI, HDR displays don't switch into HLG HDR mode.

HLG is ratified as part of BT.2100/Rec.2100 alongside PQ HDR, and is specified in ARIB STD-B67.  It can be used in both Rec 2020 and Rec 709 colour gamuts but broadcast content will almost certainly use it in the Rec 2020 gamut.

An example of HLG information from Media Info is here : 

Code:

Video
ID                                       : 1
Format                                   : HEVC
Format/Info                              : High Efficiency Video Coding
Format profile                           : Main [email protected]@Main
Codec ID                                 : hev1
Codec ID/Info                            : High Efficiency Video Coding
Duration                                 : 57mn 50s
Duration_LastFrame                       : -35ms
Bit rate                                 : 23.1 Mbps
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 25.000 fps
Standard                                 : Component
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 10 bits
Bits/(Pixel*Frame)                       : 0.111
Stream size                              : 9.32 GiB (99%)
Title                                    : 
Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                 : HLG / BT.2020 (10-bit)
Matrix coefficients                      : BT.2020 non-constant
Codec configuration box                  : hvcC

AIUI many ARM SoCs support flagging HLG in their HDMI output systems - it would be really nice if Kodi were able to flag this.

[noggin]

Good News!  The Rock64 LibreElec 8.90.009 / Kodi 18.0 RC-2-Leia is playing HLG UHD content with correctly flagged HLG EOTF.  AFAIK this is the first platform that is doing this!

Is this likely to be because the Rockchip uses a 'black box' video decoder that is just correctly handling HEVC content with Rec 2020 HLG EOTF data within the HEVC stream and outputting it independent of Kodi?  I can't see any HLG / ARIB B67 / BT.2100 code references in the Kodi GitHub (there aren't many HDR references in general that I could find when searching for BT.2100, ST.2084, HDR10, HDR, HLG, ARIB B67 etc. However I can see quite a few references to HLG and ST.2084 in the Rockchip Linux GitHub.

The content I posted the Media Info for above is playing into my Sony UHD HDR TV (which has ST.2084 HDR10, Dolby Vision Low Latency and BT.2100/ARIB STD-B67 HLG support) and switching it correctly into HLG mode.

[klosz007]

Has anyone tried playing HLG content on Kodi 18.9 on Amazon Fire TV Stick 4K (AFTV4K) ?

HLG does actually work on this AFTV4K platform - Youtube HLG videos play back fine and output HDMI signal is flagged and properly detected by A/V receiver and TV set as HLG.

BBC's Perfect Planet rips recently surpaced on torrent sites, they're encoded as HLG.
Attempt to play these files on Kodi 18.9 on AFTV4K ends up as SDR signal being sent to receiver/TV - neither A/V receiver nor TV set detect this as HLG HDR content, just as regular SDR instead.

[jjd-uk]

No form of HDR is supported on v18 so what you are seeing is correct.

[klosz007]

You meant no form of HLG HDR ? HDR10 is supported.

[jjd-uk]

For file playback v18 is SDR only if you want HDR you need to use the v19 Beta builds.