Heterogeneous Spatial Quality for Omnidirectional Video

Abstract

A video with heterogeneous spatial quality is a video where some regions of the frame have a different quality than other regions (for instance, a better quality could mean more pixels and less encoding distortion). Such a quality-variable encoding is a key enabler of Virtual Reality application, with 360-degree videos. So far, the main technique that has been proposed to prepare spatially heterogeneous quality is based on the concept of tiling. More recently, Facebook has implemented another approach: the offset projection where more emphasis is put on a specific direction of the frame. In this paper, we study quality-variable 360-degree videos with two main contributions. First, we provide the theoretical analysis of the offset projection and show the impact of the parameter settings on the video quality. Second, we propose another approach which consists in preparing the 360-degree video from a Gaussian pyramid of downscaled and blurred versions of the video. We perform an evaluation of tiling, offset and Gaussian-based approaches in representative scenarios of heterogeneous spatial quality in 360-degree videos and highlight the main trade-off to consider when implementing these approaches.

Reducing the network bandwidth requirements for 360∘ immersive video streaming

“…The choices made for the design of our strategy are motivated in the following. First, the RoI has been identified as the spherical lune because more complex strategies (such as ones employing spherical sectors) may introduce inefficiencies into the intra‐frame operations, leading to higher bitrate requirements . Moreover, maintaining the RoI at the center of the frame—applying a rotation before downscaling—allows to better exploit the motion compensation algorithm by keeping the continuity between the scaled and nonscaled areas .…”

“…A different class of approaches leverages a scaling technique to reduce the bitrate to encode the projected 360° video . In Reference , the authors propose a technique exploiting the downscaling operation to realize a specific mixed‐resolution packing for 360° video streaming.…”

“…The bitrate reduction here is achieved by varying the used quantization parameter to encode each tile, while the downscaling operation is exploited to rearrange some portion of the 360° video properly. In Reference , a Gaussian pyramid projection mapping technique is conceived to provide viewport‐adaptivity. Once the RoI is identified, the Gaussian pyramid is implemented by halving the resolution recursively in the areas around the RoI.…”

“…Differently from the approach proposed in Reference , in this letter the bitrate reduction is obtained by applying downscaling homogeneously to the regions outside the RoI. Such an approach makes the implementation considerably simpler, a particularly important aspect to empower live streaming of 360° videos.…”

Dissecting the Performance of VR Video Streaming through the VR-EXP Experimentation Platform

“…One effective strategy to reduce the huge bandwidth demands of 360-videos is delivering only the viewport in high resolution, streaming the remaining area of the video in low resolution or not at all. To achieve this spatial segmentation of the panoramic view, several approaches explore spherical-to-plane projection techniques [4,6,12,14,16,37]. For example, Graf et al [12] examine the bitrate overhead and bandwidth requirements of distinct tiling schemes (i.e., 1×1, 3×2, 5×3, 6×4, and 8×5) implemented using modern video codecs (e.g., HEVC/H.265 and VP9).…”