Page 44 - ITU Journal, ICT Discoveries, Volume 3, No. 1, June 2020 Special issue: The future of video and immersive media

ITU Journal: ICT Discoveries, Vol. 3(1), June 2020

features for supporting multiple viewpoints in the 4.2 Viewpoint switching
OMAFv2 standard are described. These facilitate
interactive content consumption and creative The OMAFv2 standard provides a versatile tool to
storytelling. leverage the possibility of switching between the
different viewpoints within the same viewpoint
4.1 Spatial relationship between multiple group or across different viewpoint groups.
viewpoints Consequently, there is a possibility to create content
based on the content creator storyline paradigm, as
Each viewpoint is represented by a spatial position well as the user preference driven switching
with respect to a common reference coordinate behavior.
system with a granularity of 10 millimeters in the
-1
3D space. This allows creating content such as the 4.2.1 Content creator specified switching
example given in Fig. 5. Having multiple viewpoints OMAFv1 supports the signaling of the default
in a contiguous space (such as a sport game or a behavior information for a viewpoint, such as
performance on a stage) benefits by having a specifying the initial viewing orientation. This
common reference coordinate system to ensure the information can be used while starting with a
individual viewpoint positions correspond to the viewpoint or after switching to a new viewpoint.
events in the content. However, this information may not be sufficient if
However, there are also scenarios where the the VR content is complex and comprises of
content may consist of some non-contiguous spaces. multiple viewpoints where not all of them may be
For example, several viewpoints which are on a available for switching at a given time, depending
sport field, while other viewpoints which cover the on the storyline needs of the content creator. For
space outside the stadium or the team locker room. example, in a scene where there are four viewpoints
This is achieved by defining multiple viewpoint (VP1, VP2, VP3 and VP4), there may be a scenario
groups, where only viewpoints in a group share a where switching from VP1 to VP3 would be possible
common reference coordinate system. Fig. 6 only after switching to VP2. To handle such a
illustrates such a scenario that comprises of four situation, OMAFv2 provides the content creator
viewpoint groups (Stadium, Locker Room 1, Locker with the tools to specify the switching candidates at
Room 2, Stadium Entrance). Furthermore, the any given time. In addition, the content creator can
standard also supports viewpoints which have a specify if a viewpoint switch occurs only as a
dynamic position, such as first-person view from a temporally seamless switch or with a temporal
race car or a flying drone. offset. Furthermore, a preferred transition effect to
be effective while switching between the two
The standard enables also the specifying of the viewpoints may also be specified by the content
geographical position and rotation offset between creator. This enables creative and interactive
the geomagnetic North and the common reference storytelling for VR content.
coordinate system. This allows any OMAFv2 player
with geolocation tracker and magnetic compass to 4.2.2 User-preference-driven switching
be located in the real world. The content creator intent is essential for consistent
experience and storytelling. However, the user choice
and exploration freedom are key aspects of a truly
immersive content experience. A scenario is
illustrated in Fig. 7 to describe the case of user-driven
viewpoint switching metadata. The content is
comprised of viewpoints VP1, VP2 and VP3, with
default initial viewing orientations Vinvo-VPi, where i=1,
2, 3. In addition, there are three objects of interest O1,
O2 and O3. The orientation of the user after switching
from one viewpoint to another viewpoint depends on
the user’s viewport orientation before performing the
viewpoint switch. The viewport orientation depends
on the object of interest the user is following. The
Fig. 6 – Example content with 4 viewpoint groups (Stadium, standard supports signaling of orientations of the
Locker Room 1, Locker Room 2, Stadium Entrance). object or person of interest while switching from a

22 © International Telecommunication Union, 2020