The Joint Collaborative Team on Video Coding (jct-vc) of itu-t wp3/16 and iso/iec jtc 1/ sc 29/ wg 11 held its tenth meeting during 11-20 July 2012 at the City Conference Centre (ccc), a k. a

5.12.5Video parameter set (VPS) and sequence parameter set (SPS) (9)

A BoG (coordinated by J. Boyce) was asked to initially review the contributions in this area along with the remaining issues in the NUH category (section 5.12.1).

JCTVC-J0550 BoG report on VPS and NAL unit header [J. Boyce]

The BoG recommended the following:

JCTVC-J0074: BoG recommended to reserve 6 NAL unit type values as VCL NAL units, and to adopt the proposed sub-bitstream extraction process (proposals #1 and #2). Decision: Agreed.

JCTVC-J0261 or JCTVC-J0546: BoG recommended to either create an SEI message to signal the active vps_id, or add the vps_id to the slice header as a fixed length field in RAP pictures. In later Track A discussion, it was suggested to do the same with the SPS ID. Another suggestion was to use a NUT. Decision: Define an SEI message that carries the following:

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  VPS ID as 4-bit FLC
  
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  A presence flag for SPS ID, then the ID itself as ue(v)
  
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  Extension data (gated by a flag or by the quantity of data in the SEI message) – detail delegated to editor.
  

A revised version of J0261 was submitted for consideration by the editors.

JCTVC-J0548 (based upon JCTVC-J0270 and JCTVC-J0272): BoG recommended an extension to the HRD parameters in VUI which duplicates some syntax elements for each temporal sub-layer. See notes on J0548 recorded elsewhere.

JCTVC-J0549 (combination of JCTVC-J0231 and JCTVC-J0250): BoG recommended to create 3 NUT values (duplicating TLA, GTLA, and coded slice) to indicate that the picture is not included in the RPS for any other picture of the same temporal sub-layer. Decision: Agreed.

As detailed in the BoG report, drawing from JCTVC-J0075, JCTVC-J0112, JCTVC-J0113, JCTVC-J0114, JCTVC-J0196, JCTVC-J0245, and JCTVC-J0257), the BoG recommended the following:

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  Move profile (profile_idc, profile_space, profile_compatability_flags, constraint_flags) from the SPS to the VPS. Decision: Add to VPS but do not remove from SPS, allow to signal for all temporal sub-layer.
  
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  Remove the following duplicated syntax elements from the SPS which are already present in the VPS: max_dec_pic_buffering, num_reorder_pics, max_latency_increase, temporal_id_nesting_flag, max_temporal_layers_minus1. In review, it was indicated that this should not include max_temporal_layers_minus1. Decision: Add to VPS but do not remove from SPS.
  
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  In VPS, optionally send profile for each lower temporal sub-layer. Yes, per above.
  
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  Send max level in VPS. level_idc still sent in SPS, may be lower than VPS max level. Decision: Agreed (level in SPS may be lower than in VPS).
  
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  In VPS, optionally send max level for each lower temporal sub-layer. Yes, per above.
  
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  In SPS, optionally send level for each lower temporal sub-layer, may be lower than corresponding VPS max level. Decision: Agreed (level in SPS may be lower than in VPS).
  
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  In VPS, used fixed length coding for the syntax elements at the beginning of the VPS. This implies decisions about what range of values to apply. The VPS ID is proposed to be 4 bit FLC. Decision: Agreed.
  
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  In VPS, add a byte pointer following fixed length syntax elements and before first ue(v) coded syntax elements. In discussion, it was suggest to change this to just a reserved syntax element, e.g. reserved_zero_12bits. Decision: Agreed.
  
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  In NAL unit header, remove nal_ref_flag, and allocate bit to reserved bits. Reorder syntax elements in NUH so that all 6 reserved bits are contiguous and immediately follow the NUT. Decision: Agreed.
  
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  Change temporal_id to temporal_id_plus1 and change the prescribed value of reserved_one_5bits (i.e. layer_id_plus1) to 0. Decision: Agreed.
  

The BoG encourageds further study on moving the SPS VUI HRD parameters to the VPS. A problem as identified that there are no clear HRD performance specified when bitstreams with enhancement layers are fed to a decoder conforming to the base specification. The BoG recommended to revisit further discuss JCTVC-J0562 as a potential solution.

Tues 1430 discussion:

Regarding duplication

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  profile & level (multi temporal layers).
  
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  high-level CVS characteristics (5 syntax elements: max_dec_pic_buffering, num_reorder_pics, max_latency_increase, temporal_id_nesting_flag, max_temporal_layers_minus1) (the first 3 being at multi temporal layers).
  
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  HRD parameters (multi temporal layers).
  

Suggestion:

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  Put sequence_characteristics_present_flag in SPS.
  
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  Specify that the flag shall be equal to 1 for the Main profile.
  
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  In some extension the flag could be equal to 0.
  

It was asked whether it would it be difficult to support the case where the hypothetical flag is equal to 0.

Comment: The flag isn't actually necessary, because the presence could be conditioned on the layer id.

Comment: We could the VPS characteristics to be "over-written" by lower-capability characteristics in the SPS when the flag is 1 – e.g. in a layer-specific IDR.

Comment: There is a related contribution J0245 to put sub-bitstream characteristics in an SEI message.

No consensus to remove syntax elements from SPS that are put into the VPS.

Other aspects of BoG report were then re-reviewed and closed. Then, at 1600, J0562, and then 3V were discussed.