26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS
An overlay is defined as a piece of visual media, rendered over omnidirectional video or on the viewport. An ITT4RT-Tx client supporting the ‘Overlay’ feature shall add real-time overlays on top of a 360-degree background and offer this capability in the SDP as part of the the initial offer-answer negotiation. An overlay in ITT4RT is characterized by the overlay source and its rendering configuration. ITT4RT supports both 2D and spherical overlays.
An overlay source specifies the image or video to be used as the content for the overlay. The overlay source is a bitstream that may be delivered as an overlay video encoded and delivered as an RTP stream.
ITT4RT clients supporting the ‘Overlay’ feature have the following requirements:
– an ITT4RT-Tx client may be capable to provide a bitstream consisting of an overlay with a video source that conforms to the requirements of Y.3 or the video bitstream requirements of MTSI.
– an ITT4RT-Tx client may be capable of providing HEVC encoded images/image sequence that conform to HEVC bitstream requirements of Y.3. The signalling for such a stream shall comply to 6.2.11 and 7.4.8.
– an ITT4RT-Rx client may be capable to decode and render a 360-degree video bitstream and further decode and render one or more overlay streams on top of the 360-degree video.
The rendering configuration defines how the overlay is to be rendered in the spherical scene. It is possible for an overlay to be delivered without any rendering configuration, in which case, the ITT4RT-Rx client should render the content as per the default configuration described in section Y.6.4.3. Alternatively, the rendering configuration for one or more overlays may be negotiated during session establishment to ensure uniform operation for different receivers.