Flattening the Earth, Two Thousand Years of Map Projections

In this survey, we present state-of-the-art bitrate adaptation algorithms for HTTP adaptive streaming (HAS). As a key distinction from other streaming approaches, the bitrate adaptation algorithms in HAS are chiefly executed at each client, i.e. , in a distributed manner. The objective of these algorithms is to ensure a high quality of experience (QoE) for viewers in the presence of bandwidth fluctuations due to factors like signal strength, network congestion, network reconvergence events, etc. While such fluctuations are common in public Internet, they can also occur in home networksor even managed networks where there is often admission control and QoS tools. Bitrate adaptation algorithms may take factors like bandwidth estimations, playback buffer fullness, device features, viewer preferences, and content features into account, albeit with different weights. Since the viewer’s QoE needs to be determined in real-time during playback, objective metrics are generally used including number of buffer stalls, duration of startup delay, frequency and amount of quality oscillations, and video instability. By design, the standards for HAS do not mandate any particular adaptation algorithm, leaving it to system builders to innovate and implement their own method. This survey provides an overview of the different methods proposed over the last several years.

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A Survey on Bitrate Adaptation Schemes for Streaming Media Over HTTP

While Virtual Reality applications are increasingly attracting the attention of developers and business analysts, the behaviour of users watching 360-degree (ie omnidirectional) videos has not been thoroughly studied yet This paper introduces a dataset of head movements of users watching 360-degree videos on a Head-Mounted Display (HMD) The dataset includes data collected from 59 users watching five 70 s-long 360-degree videos on the Razer OSVR HDK2 HMD The selected videos span a wide range of 360-degree content for which different viewer's involvement, thus navigation patterns, could be expected We describe the open-source software developed to produce the dataset and present the test material and viewing conditions considered during the data acquisition Finally, we show some examples of statistics that can be extracted from the collected data, for a content-dependent analysis of users' navigation patterns The source code of the software used to collect the data has been made publicly available, together with the entire dataset, to enable the community to extend the dataset

360-Degree Video Head Movement Dataset

The delivery and display of 360-degree videos on Head-Mounted Displays (HMDs) presents many technical challenges. 360-degree videos are ultra high resolution spherical videos, which contain an omnidirectional view of the scene. However only a portion of this scene is displayed on the HMD. Moreover, HMD need to respond in 10 ms to head movements, which prevents the server to send only the displayed video part based on client feedback. To reduce the bandwidth waste, while still providing an immersive experience, a viewport-adaptive 360-degree video streaming system is proposed. The server prepares multiple video representations, which differ not only by their bit-rate, but also by the qualities of different scene regions. The client chooses a representation for the next segment such that its bit-rate fits the available throughput and a full quality region matches its viewing. We investigate the impact of various spherical-to-plane projections and quality arrangements on the video quality displayed to the user, showing that the cube map layout offers the best quality for the given bit-rate budget. An evaluation with a dataset of users navigating 360-degree videos demonstrates that segments need to be short enough to enable frequent view switches.

Viewport-Adaptive Navigable 360-Degree Video Delivery

https://hal.archives-ouvertes.fr/hal-01574040/document

Viewport-adaptive navigable 360-degree video delivery

Delivering wide-angle and high-resolution spherical panoramic video content entails a high streaming bitrate. This imposes challenges when panorama clips are consumed in virtual reality (VR) head-mounted displays (HMD). The reason is that the HMDs typically require high spatial and temporal fidelity contents and strict low-latency in order to guarantee the user's sense of presence while using them. In order to alleviate the problem, we propose to store two versions of the same video content at different resolutions, each divided into multiple tiles using the High Efficiency Video Coding (HEVC) standard. According to the user's present viewport, a set of tiles is transmitted in the highest captured resolution, while the remaining parts are transmitted from the low-resolution version of the same content. In order to enable randomly choosing different combinations, the tile sets are encoded to be independently decodable. We further study the trade-off in the choice of tiling scheme and its impact on compression and streaming bitrate performances. The results indicate streaming bitrate saving from 30% to 40%, depending on the selected tiling scheme, when compared to streaming the entire video content.

HEVC-compliant Tile-based Streaming of Panoramic Video for Virtual Reality Applications

Virtual reality applications use 360-degree videos and head mount displays (HMDs) with stereoscopic capabilities to provide full immersion experience. In these applications it is also common to use 4K resolution or higher per view for 360-degree videos. Consequently, this leads to technical challenges in handling the bandwidth requirements while keeping the system latency to the minimal. When the content is viewed with a HMD, a subset of the entire 360-degree video is displayed at a single point of time. To improve the resolution and picture quality of the displayed content, viewport based coding is desirable. In this regard, we investigated various viewport dependent projection schemes including the existing variants of Pyramidal projection. In this regard we propose the multi-resolution versions of Equirectangular and Cubemap projections. Additionally, we developed a methodology for comparing the rate-distortion performance of these projections. Based on the simulation results, it was observed that multi-resolution projections of Equirectangle and Cubemap outperform other projection schemes, significantly.

Viewport-Adaptive Encoding and Streaming of 360-Degree Video for Virtual Reality Applications

Pseudo-cylindrical panoramas represent the data distribution of spherical coordinates closely in two-dimensional domain due to the equidistant sampling of 360-degree scene. Therefore, unlike the cylindrical projections, they do not suffer from the over stretching in the polar areas. However, due to the non-rectangular format in effective picture area and sharp edges at its borders, the compression performance is inefficient. In this paper, we propose two methods which improve the compression performance of both intra-frame and inter-frame coding of pseudo-cylindrical panoramic content and meanwhile reduce the coding artifacts. In the intra-frame coding method, border edges are smoothed by modifying the content of the image in the non-effective picture area, which are cropped at the receiver side. In the inter-frame coding method, gaining the benefit of 360-degree property of the content, non-effective picture area of reference frames at border is filled with the content of the effective picture area from the opposite border to enhance the performance of motion compensation.

Efficient Coding of 360-Degree Pseudo-Cylindrical Panoramic Video for Virtual Reality Applications

In order to compress omnidirectional video clips, a projection onto a two-dimensional image plane is necessary. The most commonly used projection format is the equirectangular panoramic projection, which results into a significant amount of redundant samples in the polar areas. The redundant samples incur extra bitrate and increase the encoding/decoding time. In this paper, we study regional down-sampling (RDS) for achieving better compression and smaller encoding/decoding time for omnidirectional content. We extend the persistent RDS method applied equally to all pictures to be applied to selected pictures only in our proposed temporal RDS method and then compare the persistent and temporal RDS methods. The simulation results indicate that both the persistent and temporal RDS improve the rate-distortion (RD) performance compared to the conventional coding of equirectangular panoramas, while the temporal RDS method has less sequence-wise RD performance variation and slightly better RD performance on average when compared to the persistent RDS technique. Alongside the coding methods, we study spherical quality measurement methods for VR images/video and analyze the coding methods with these quality metrics. Moreover, we propose a uniformly sampled spherical quality metric in order to evaluate the coding distortion of omnidirectional videos.

Analysis of regional down-sampling methods for coding of omnidirectional video

Virtual reality (VR) head-mounted display (HMD) requires spherical panoramic contents with high-spatial and temporal fidelity to immerse the viewers into the captured scene Hereby, VR contents are extremely bandwidth intensive and impose technical challenges for the design of a VR streaming system A bandwidth-efficient VR streaming system can be achieved using the viewport-aware adaptation techniques, in which part of the sphere within the viewer's field of view is presented at higher quality In this paper, two recently emerged viewport-adaptive streaming methods so-called tile-based method and truncated square pyramid (TSP) projection, a well-studied viewport-dependent projection, are compared using a proposed quality assessment methodology The comparison is made in terms of storage and streaming bitrate performances The simulation results indicate that the tile-based approach has slightly lower streaming performance, while offering a significant storage and encoding time saving at the server side, compared to TSP-based streaming

Alireza Aminlou

Papers

HEVC-compliant Tile-based Streaming of Panoramic Video for Virtual Reality Applications

Viewport-Adaptive Encoding and Streaming of 360-Degree Video for Virtual Reality Applications

Efficient Coding of 360-Degree Pseudo-Cylindrical Panoramic Video for Virtual Reality Applications

Analysis of regional down-sampling methods for coding of omnidirectional video

Virtual reality content streaming: Viewport-dependent projection and tile-based techniques