Y.7 Media transport

26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS

Y.7.1 RTP

RTP signaling impacts are FFS.

Y.7.2 RTCP

When viewport-dependent processing (VDP) of 360-degree video is successfully negotiated between the ITT4RT-Tx client and ITT4RT-Rx client as per the SDP-based procedures described in clause Y.6.2, the RTCP feedback (FB) message type ‘Viewport’ shall carry requested viewport information during the RTP transmission of media signalled from the ITT4RT-Rx client to the ITT4RT-Tx client.

The signalling of ‘Viewport’ requests shall use RTCP feedback messages as specified in IETF 4585. The RTCP feedback message is identified by PT (payload type) = PSFB (206) which refers to payload-specific feedback message. FMT (feedback message type) shall be set to the value ‘X’ for Viewport feedback messages. The IANA registration information for the FMT value for ‘Viewport’ is provided in Annex R.1 of TS 26.114. The RTCP feedback method may involve signalling of viewport information in both of the immediate feedback and early RTCP modes.

The FCI (feedback control information) format for Viewport shall be as follows. The FCI shall contain exactly one viewport. The signalled desired viewport information in the RTCP feedback message for ‘Viewport’ is composed of the following parameters (as defined as shape type value equal to 0 in clause 7.5.6 of ISO/IEC 23090-2 [179]):):

– Viewport_azimuth: Specifies the azimuth of the centre point of the sphere region corresponding to the requested viewport in units of 2⁻¹⁶ degrees relative to the global coordinate axes expressed in signed 32-bit integer format, in the range of −180 * 2¹⁶ to 180 * 2¹⁶ − 1, inclusive..

– Viewport_elevation: Specifies the elevation of the centre point of the sphere region corresponding to the requested viewport in units of 2⁻¹⁶ degrees relative to the global coordinate axes expressed in signed 32-bit integer format, in the range of −90 * 2¹⁶ to 90 * 2¹⁶, inclusive.

– Viewport_tilt: Specifies the tilt angle of the sphere region corresponding to the requested viewport, in units of 2⁻¹⁶ degrees, relative to the global coordinate axes expressed in signed 32-bit integer format, in the range of −180 * 2¹⁶ to 180 * 2¹⁶ − 1, inclusive.

– Viewport_azimuth_range: Specifies the azimuth range of the sphere region corresponding to the requested viewport through the centre point of the sphere region in units of 2⁻¹⁶ degrees expressed in unsigned 32-bit integer format, in the range of 0 to 180 * 2¹⁶, inclusive.

– Viewport_elevation_range: Specifies the elevation range of the sphere region corresponding to the requested viewport through the centre point of the sphere region in units of 2⁻¹⁶ degrees expressed in unsigned 32-bit integer format, in the range of 0 to 180 * 2¹⁶, inclusive.

The RTCP feedback message for ‘Viewport’ shall contain all of the parameters Viewport_azimuth, Viewport_elevation, Viewport_tilt, Viewport_azimuth_range and Viewport_elevation_range. The values for the each of the parameters Viewport_azimuth, Viewport_elevation, Viewport_tilt, Viewport_azimuth_range and Viewport_elevation_range shall each be indicated using four bytes.

The FCI for the RTCP feedback message for ‘Viewport’ shall follow the following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Viewport_azimuth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Viewport_elevation |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Viewport_tilt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Viewport_azimuth_range |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Viewport_elevation_range |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

For each 4-byte indication of the Viewport_azimuth, Viewport_elevation, Viewport_tilt, Viewport_azimuth_range and Viewport_elevation_range, the bytes will be ordered in the order of importance such that high bytes shall be followed by the low bytes, where the highest byte holds the most significant bits and lowest byte holds the least significant bits.