  To deliver ultra-high resolution 360-degree video (such as 8K, 12K, or even
higher) across the internet, viewport-dependent streaming becomes necessary to
save bandwidth. During viewport switches, clients and servers will instantly
exchange coordination info and contents for the given viewports. However, those
viewport switches pose a serious challenge for video encoding because the
temporal dependency between contents within changing viewports is
unpredictable. In existing practices, it is commonly noted that GOP (Group of
Pictures) size in a bitstream intrinsically prohibits the reduction of the
viewport switch latency, such as Motion-to-photon (MTP) latency, or
motion-to-high-quality (MTHQ) latency. In this paper, we presented a Scalable
Video Coding (SVC) based bitstream schema, which can structurally remove the
impacts of GOP in viewport-dependent streaming and provide instant viewport
switches within one-frame time (the best possible). In addition, combined with
tiling, this new coding schema allows an efficient packing of the non-adjacent
regions within a viewport of 360-degree video. Our experiments also show that
the overall encoding with this SVC-based approach is faster than with
multi-stream approaches. Compared with current 360-degree video streaming
solutions based on MPEG-I OMAF, our approach is superior in terms of viewport
switch latency, simplicity of viewport packing, and encoding performance.
