On HLS VIDEO-RANGE

[podborski]

Moving my comment to an issue as discussed during the meeting.

The group had some discussion on the color box and codecs string handling in combination with the signaling from the Sequence Header OBU. Maybe one more thing to consider is that the HLS spec. also defines a VIDEO-RANGE as:

VIDEO-RANGE definition

VIDEO-RANGE

  The value is an enumerated-string; valid strings are SDR, HLG and
  PQ.

  The value MUST be SDR if the video in the Variant Stream is
  encoded using one of the following reference opto-electronic
  transfer characteristic functions specified by the
  TransferCharacteristics code point: [[CICP](https://datatracker.ietf.org/doc/html/draft-pantos-hls-rfc8216bis#ref-CICP)] 1, 6, 13, 14, 15.  Note
  that different TransferCharacteristics code points can use the
  same transfer function.

 The value MUST be HLG if the video in the Variant Stream is
  encoded using a reference opto-electronic transfer characteristic
  function specified by the TransferCharacteristics code point 18,
  or consists of such video mixed with video qualifying as SDR (see
  above).

  The value MUST be PQ if the video in the Variant Stream is encoded
  using a reference opto-electronic transfer characteristic function
  specified by the TransferCharacteristics code point 16, or
  consists of such video mixed with video qualifying as SDR or HLG
  (see above).

  This attribute is OPTIONAL.  Its absence implies a value of SDR.
  Clients that do not recognize the attribute value SHOULD NOT
  select the Variant Stream.

I think it would be useful if we at least add a note, mentioning that care needs to be taken as the VIDEO-RANGE attribute in HLS groups certain transfer characteristics CICP values into 3 buckets (SDR,HLG,PQ) and codecs string is signaling similar information.

One could argue that this is responsibility of the HLS spec to clarify this, but maybe it does not harm to also add a note in this spec?

[wantehchang]

Hi Dimitri,

The HLS spec. you linked to is still an Internet-Draft. Should we wait until it has become an RFC to add this note?

[podborski]

I'm not so much familiar with the IETF processes but we always use the most recent version of the draft standard in our guidelines. For example here: HTTP Live Streaming (HLS) authoring specification for Apple devices we have a requirement for non SDR:

9.16. The VIDEO-RANGE attribute MUST be specified unless all variants and renditions are SDR.

But I'll ask Roger about the IETF publishing process.