JVET-R0046 AHG8: Temporal sublayer requirements for multi-layer referencing [C.-Y. Lai, O. Chubach, C.-Y. Chen, T.-D. Chuang, Y.-W. Huang, S.-M. Lei (MediaTek)]
In the adopted JVET-Q0398, the goal of max_tid_il_ref_pics_plus1[ i ] is to achieve decoding a higher layer without full decoding of all temporal sublayers of a lower layer when inter-layer prediction is used. However, only the reconstructed pictures are considered in JVET-Q0398, while picture parameter set (PPS), adaptation parameter set (APS), and reference picture list (RPL) are not considered in this document. In this contribution, two aspects are proposed to change this aspect of the current design in VVC Draft 8.
The first aspect is to add bitstream conformance requirements for PPS-related syntax elements and APS-related syntax elements in picture header (PH) or slice header according to max_tid_il_ref_pics_plus1[ i ].
The second aspect is to add a bitstream conformance requirement for the RPL construction.
The contributor said this contribution is compatible with JVET-R0193.
It was commented that since PSs can be conveyed by external means, it may not be possible to require them to be associated with a particular AU or PU.
Subclause C.6 of HEVC for subbitstream extraction was discussed. There was a sentence saying to “Remove from outBitstream all NAL units for which all of the following conditions are true”. It was discussed whether this should be “all NAL units” or “all VCL NAL units”, and generally what happens to PSs in this extraction process.
AfterA offline study, the first aspect was further discussed on 23 April at 0825; modified text was provided in a revision of the contribution. Instead of adding constraints, the description of the bitstream extraction process was changed.
Decision (expression of existing intent): Adopt aspect 1.2 per -v4 version of the contribution.
For the second aspect, to make the specification clearer, and to avoid confusion in the decoding process for RPL construction, it is proposed to add a bitstream conformance requirement as follows.
Decision (expression of existing intent): Add a requirement of bitstream conformance that the picture referred to by each ILRP entry in RefPicList[ 0 ] or RefPicList[ 1 ] of a slice of the current picture shall be an IRAP picture or shall have TemporalId less than or equal to Max(0, max_tid_il_ref_pics_plus1[ refPicVpsLayerId ] − 1), with refPicVpsLayerId equal to the value of the nuh_layer_id of the referenced picture.