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      <base href="https://bugzilla.libav.org/" />
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - HEVC: backwards compatible HDR/HLG signalling not supported"
   href="https://bugzilla.libav.org/show_bug.cgi?id=1097">1097</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>HEVC: backwards compatible HDR/HLG signalling not supported
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>Libav
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>git HEAD
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>---
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>libavcodec
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>bugzilla@libav.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>basic.master@gmx.de
          </td>
        </tr></table>
      <p>
        <div>
        <pre>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
19,2E.

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.*</pre>
        </div>
      </p>
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