Content for  TS 26.118  Word version:  18.0.0

This operation point targets simple deployments and legacy receivers at basic quality. A full 360-degree video signal with equirectangular projection following the 3GPP reference system may be provided to the decoding and rendering system for immediate decoding and rendering. Note that this operation point enables to distribute 4k video at regular frame rates and 3k video at higher frame rates. Restricted coverage is supported as well, but only in a basic and backward-compatible fashion. A Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation point shall conform to the requirements in the remainder of clause 5.1.4. A receiver conforming to the 3GPP VR Basic H.264/AVC Operation point shall support decoding and rendering a Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation point. Detailed receiver requirements are provided in the remainder of clause 5.1.4.

A Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation point shall conform to H.264/AVC Progressive High Profile Level 5.1 [5] for H.264/AVC with the following additional restrictions and requirements:

• the maximum VCL Bit Rate is constrained to be 120 Mbps with cpbBrVclFactor and cpbBrNalFactor being fixed to be 1250 and 1500, respectively.
• the bitstream does not contain more than 10 slices per picture.

Hence, for a Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation point, the following applies:

• The profile_idc shall be set to 100 indicating the High profile.
• The constrain_set0_flag, constrain_set1_flag, constrain_set2_flag and constrain_set3_flag shall all be set to 0.
• The value of level_idc shall not be greater than 51 (corresponding to the level 5.1) and should indicate the lowest level to which the Bitstream conforms.

Picture aspect ratio 2:1 should be used for the encoded picture. The spatial resolution of the original format in equirectangular projection (ERP) should be one of the following (expressed in luminance pixel width × luminance pixel height):

• 4096 × 2048, 3840 × 1920, 3072 × 1536, 2880 × 1440, 2048 × 1024.

The spatial resolution of the distribution format should be one of the following (expressed in luminance pixel width × luminance pixel height):

• 3840 × 1920, 2880 × 1440, 1920 × 960, 1440 × 720, 960 × 480.
• 4096 × 2048, 3072 × 1536, 2048 × 1024, 1536 × 768, 1024 × 512.

A Receiver conforming to the 3GPP VR Basic H.264/AVC Operation Point shall be capable of decoding and rendering Bitstreams that contain spatial resolutions as above.

A Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation Point shall use Recommendation ITU-R BT.709 [3] colorimetry. Hence, in the VUI, the colour parameter information shall be present, i.e.

• video_signal_type_present_flag value and colour_description_present_flag value shall be set to 1.
• The colour_primaries value, the transfer_characteristics value and the matrix_coefficients value in the Video Usability Information shall all be set to 1.

A Receiver conforming to the 3GPP VR Basic H.264/AVC Operation Point shall be capable of decoding and rendering Bitstreams that use Recommendation ITU-R BT.709 [3] colorimetry according to the bitstream requirements documented above.

A Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation Point shall have one of the following frame rates: 24; 25; 30; 24/1001; 30/1001; 50; 60; 60/1001 Hz. The profile and level constraints of H.264/AVC Progressive High Profile Level 5.1 require careful balance of the permitted frame rates and spatial resolutions. Table 5.1-2 provides the permitted combinations of spatial resolutions and frame rates.

In the VUI, the timing information may be present:

• If the timing information is present, i.e. the value of timing_info_present_flag is set to 1, then the values of num_units_in_tick and time_scale shall be set according to the frame rates allowed above. The timing information present in the video Bitstream should be consistent with the timing information signalled at the system level.
• The frame rate shall not change between two RAPs. fixed_frame_rate_flag value shall be set to 1.

A Receiver conforming to the 3GPP VR Basic H.264/AVC Operation Point shall be capable of decoding and rendering Bitstreams that use frame rates according to the bitstream requirements documented above.

For H.264/AVC random access point (RAP) definition refer to clause 4.4.1.1 of TS 26.116. RAPs shall be present in the Bitstream at least once every 5 seconds. It is recommended that RAPs occur in the video Bitstream on average at least every 2 seconds. The time interval between successive RAPs is measured as the difference between their respective decoding time values.

The following restrictions apply to the active Sequence Parameter Set (SPS):

• gaps_in_frame_num_value_allowed_flag value shall be set to 0.
• The Video Usability Information shall be present in the active Sequence Parameter Set. The vui_parameter_present_flag shall be set to 1.
• The source video format shall be progressive. frame_mbs_only_flag shall be set to 1 for every picture of the Bitstream.

In addition to the previous constraints on the VUI on colour information in clause 5.1.4.4 and on frame rates in clause 5.1.4.5, this clause contains further requirements. The aspect ratio information shall be present, i.e.

• The aspect_ratio_present_flag value shall be set to 1.
• The aspect_ratio_idc value shall be set to 1 indicating a square pixel format.

There are no requirements on output timing conformance for H.264/AVC decoding (Annex C of [5]). The Hypothetical Reference Decoder (HRD) parameters, if present, should be ignored by the Receiver.

This operation point uses equirectangular projection, such the video is automatically rendered in the 3GPP reference system. This is enabled by using the MPEG metadata on equirectangular projection. A Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation Point shall include the equirectangular projection SEI message (payloadType equal to 150) at every RAP. The erp_guard_band_flag shall be set to 0. A Receiver conforming to the 3GPP VR Basic H.264/AVC Operation Point shall be able to process the information contained on equirectangular projection SEI message (payloadType equal to 150) with erp_guard_band_flag shall be set to 0.

This operation point permits the decoding and rendering of restricted coverage video signals in a rudimentary way. In this case it is expected that pixels that are projected to a non-covered region are included in the full image, but are visually differentiated from the covered region, for example using black, grey or white colour. Application or system-based signalling may support signalling the coverage region.

For a Bitstream conforming to the 3GPP VR Basic H.264/AVC Operation Point:

• the equirectangular projection SEI message (payloadType equal to 150) with erp_guard_band_flag not set to 0 shall not be present,
• the sphere rotation SEI message (payloadType equal to 154) shall not be present,
• the region-wise packing SEI message (payloadType equal to 155) shall not be present,
• the frame-packing arrangement SEI message (payloadType equal to 45) shall not be present.

Receivers conforming to the 3GPP VR Basic H.264/AVC Operation Point shall support decoding and displaying 3GPP VR Basic H.264/AVC Operation Point Bitstreams. Receivers conforming to the 3GPP VR Basic H.264/AVC Operation Point shall support all Receiver requirements in clause 5.1.4.