ILRP in case of vps_max_tid_il_ref_pics_plus1[ i ][ j ] equal to 0

[ochubach]

From the syntax semantics of vps_max_tid_il_ref_pics_plus1[ i ][ j ]: if vps_max_tid_il_ref_pics_plus1[ i ][ j ] is equal to 0, only IRAP or GDR pictures with ph_recovery_poc_cnt equal to 0 can be used as ILRP.

But in RPL, if vps_max_tid_il_ref_pics_plus1[ i ][ j ] is equal to 0, not only IRA and GDR but also picture with temporal ID equal to 0 can be used as ILRP, because of this description: The picture shall have TemporalId less than or equal to Max( 0, vps_max_tid_il_ref_pics_plus1[ currLayerIdx ][ refLayerIdx ] − 1 ), where currLayerIdx and refLayerIdx are equal to GeneralLayerIdx[ nuh_layer_id ] and GeneralLayerIdx[ refpicLayerId ], respectively.

[ochubach]

It is proposed to change the description in the RPL as follows:
"The picture shall have TemporalId less than vps_max_tid_il_ref_pics_plus1[currLayerIdx][refLayerIdx], where currLayerIdx and refLayerIdx are equal to GeneralLayerIdx[nuh_layer_id] and GeneralLayerIdx[refpicLayerId], respectively."
This way, the constraint will be matching with the syntax semantics of vps_max_tid_il_ref_pics_plus1[][].

[yk]

I think your suggestion is correct. But I am not closing the ticket now, such that we can have a discussion soon in the tickets reviewing session, just to be safe.

[ysanchez]

I think there is an issue with the suggested change. Currently when vps_max_tid_il_ref_pics_plus1[ i ][ j ] is equal to 0 the constraint says that the reference picture shall have a TermporalId less or equal to 0. This is correct. We are not saying that it can only be an IRAP or GDR with ph_recovery_poc_cnt equal to 0, but this is expressed in the semantics.

The suggested change would result in: "The picture shall have TemporalId less than 0", which is not correct.

[yk]

Thanks! The original suggestion was confirmed at a JVET meeting session and has been fixed in S2001-v6.