[libav-bugs] [Bug 1097] New: HEVC: backwards compatible HDR/HLG signalling not supported

bugzilla at libav.org bugzilla at libav.org
Fri Oct 27 20:32:26 CEST 2017


https://bugzilla.libav.org/show_bug.cgi?id=1097

            Bug ID: 1097
           Summary: HEVC: backwards compatible HDR/HLG signalling not
                    supported
           Product: Libav
           Version: git HEAD
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: ---
         Component: libavcodec
          Assignee: bugzilla at libav.org
          Reporter: basic.master at gmx.de

An HEVC video stream can include HDR information using e.g. HLG. Due to the
nature of HLG, such a video stream looks good also on SDR devices.

There are two ways to signal HLG:
#1 Non-backwards compatible with SDR devices
- the VUI field "transfer_characteristics" is set to 18 (= ITU-R BT.2100 HLG)

#2 Backwards compatible with SDR devices
- the VUI field "transfer_characteristics" is set to 14 (= ITU-R BT.2020)
- the HEVC contains an "Alternative transfer characteristics" (type 147) SEI
message at RAPs, with the field "preferred_transfer_characteristics" set to 18
(= ITU-R BT.2100 HLG)

Libav currently only supports #1. So a stream using #2 is not recognized as
HDR/HLG.

However #2 is used much more often, as it is required by DVB (see clause
5.14.4.4.2.1 in ETSI TS 101 154 v2.3.1); see the HDR test streams on Astra
19,2°E.

Note that FFmpeg already processes the described SEI and supports #2 (in
addition to #1), so it might be easier to adopt its implementation somehow. See
/libavcodec/hevc_sei.*

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