JVET-AL0118 AHG9: Miscellaneous changes for the three DSC SEI messages [Y.-K. Wang, J. Xu (Bytedance), Y. Li, K. Yang, Y. Xu (SJTU)]

This contribution proposes the following changes for three digitally signed content (DSC) SEI messages, namely the digitally signed content initialization (DSCI) SEI message, the digitally signed content selection (DSCS) SEI message, and the digitally signed content verification (DSCV) SEI message:

1. Add definitions of GDR picture and GDR AU, update the definition of IRAP AU accordingly, and change the constraint on presence of DSCI SEI messages to be: When a DSCI SEI message with a particular dsci_id value dscIdVal is present in any AU of a CVS, a DSCI SEI message with dsci_id equal to dscIdVal shall be present in each IRAP or GDR AU in the CVS.
2. Replace the asserted unclear constraint on content of DSCI or DSCV SEI messages with the following: All DSCV SEI messages having a particular value of dscv_id and a particular value of dscv_vss_id in a verification period for dsci_id equal to the particular value of dscv_id shall have the same content.
3. Add the DSC ID aspect to the constraint on presence of DSCS SEI messages so that it becomes the following: When a CVS does not contain a DSCI SEI message with a particular dsci_id value dscIdVal, the CVS shall not contain a DSCS SEI message with dscs_id equal to dscIdVal.
4. Infer the value of dscs_id to be equal to the dsci_id of the associated DSCI SEI message (instead of to be equal to 0) when a DSCS SEI message is not present in a PU.
5. Add the following constraint on relative order between DSCS and DSCV SEI messages in an AU: When an AU contains a DSCS SEI message with dscs_id equal to dscIdA and dscs_vss_id equal to vssIdA and a DSCV SEI message with dscv_id equal to dscIdA and dscv_vss_id equal to vssIdA, the DSCS SEI message shall precede the DSCV SEI message in decoding order.
6. Change the constraint on absence of relevant verification NAL units after the current DSCV SEI message to be after the current PU, such that the constraint becomes the following: Within the current verification period, there shall be no verification NAL unit of the verification substream with verification substream ID equal to dscv_vss_id succeeding the current PU in decoding order.
7. Change the derivation of reference digests for fixing two asserted bugs.
8. Clarify that all concatenation operations of verification NAL units and, when needed, reference digests, for obtaining a message used for calculating the message digest, or for constructing the identification string for a verification substream, are performed in decoding order for verification NAL units and in increasing order of refIdx for reference digests.

The discussions and the detailed proposed changes are based on the spec text provided in JVET-AL0103, which includes asserted purely editorial changes to the DSC SEI messages based on JVET-AK2006-v1.

In -v2 of this contribution, for item 7 a different proposed change was included for fixing the two asserted bugs.

Proposal 1 agreed, with the wording of the definition of IRAP is suggested to be changed to replace “and” with “such that when”. The exact language is delegated to the editors.

Proposal 2 identifies an unclear constraint on content of DSCI or DSCV SEI messages. Related proposals in JVET-AL0222 and JVET-AL0131 identify the same problem but propose a different spec change to address.

Agreed to remove the constraint.

Proposal 3 agreed.

Proposal 4 is related to side activity.

Proposal 5 agreed.

Proposal 6 is already covered in JVET-AL0103-v3.

For proposal 7, it is suggested that some constraint may be needed, and to possibly add language “in the current verification period” in the determination of the reference digest.

Further discussion requested on proposal 7.

Proposal 8 agreed.

Decision: adopt to VSEI v4 as noted above.

Proposal 7 further discussed 1630 on Tuesday 1 April 2025.

Decision: Adopt proposal 7.