Search

Omnidirectional MediA Format (OMAF), a recent standard for representation of 360° video content, supports only equirectangular projection (ERP) and cubemap projection (CMP) and their region-wise packing with a 4K decoding-capability constraint on the end-user devices. Streaming of 4K content allows only a limited viewport resolution, which is lower than the resolution of many current head-mounted displays (HMDs). Two 6K-effective multi-resolution packing schemes for ERP and CMP are recommended by the OMAF standard, which take full advantages of HMDs with quad HD resolution while sticking with 4K-decoding constraint. This paper studies and compares the performance of these two packings in the context of viewport-adaptive streaming using the High Efficiency Video Coding (HEVC) standard and Zonal-PSNR test methodology. Overall, the experimental results show that rate-distortion performance of both packings sequence wise mixed but similar in average.

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.

Most existing quality metrics do not take the human attention analysis into account. Attention to particular objects or regions is an important attribute of human vision and perception system in measuring perceived image and video qualities. This paper presents an approach for extracting visual attention regions based on a combination of a bottom-up saliency model and semantic image analysis. The use of PSNR (Peak Signal-to-Noise Ratio) and SSIM (Structural SIMilarity) in extracted attention regions is analyzed for image/video quality assessment, and a novel quality metric is proposed which can exploit the attributes of visual attention information adequately. The experimental results with respect to the subjective measurement demonstrate that the proposed metric outperforms the current methods.

Subjective quality evaluation is used to optimize the produced audiovisual quality from fundamental signal processing algorithms to consumer services. These studies typically follow the basic principles of controlled psychoperceptual experiments. However, when compromising compression and transmission parameters for consumer services, the ecological validity of conventional quality evaluation methods can be questioned. To tackle this, we firstly present a novel user-oriented quality evaluation method for mobile television in its usage contexts. Secondly, we present the results of an experiment conducted with 30 participants comparing acceptability and satisfaction of quality as well as goals of viewing in three mobile contexts and under four different residual transmission error rates, when the participants also performed simultaneous assessment tasks. Finally, we compare the results with a previous laboratory experiment. The studied error rates impacted negatively on all measured tasks with some contextual differences. Moreover, the evaluations were more favorable and less discriminate in the mobile contexts compared to the laboratory.

Mobile video applications are becoming more and more popular. This paper presents an overview of the most important mobile video application standards, including multimedia messaging service (MMS), streaming, video telephony, and multicast and broadcast. In addition, the video coding standards for mobile video applications are reviewed. Selected systems aspects of video coding, including error robustness, latency and bitrate variation as well as scalability, which are important for mobile video applications, are also discussed.

This paper proposes two encoding methods for discardable slices in scalable video coding. Discardable slices are not used for inter-layer prediction and can therefore be removed from a coded bitstream from layers below the decoded scalable layer. Consequently, discardable slices need not be transmitted when the layer that the receiver decodes is known by the sender. The potential bit rate saving compared with conventional scalable coding makes the use of discardable slices an attractive encoding strategy, e.g. for unicast streaming applications. Among the two proposed encoding algorithms, one is a two-pass encoding method and the other models the coding problem as a Knapsack Problem (KP). Performed simulations indicate improved rate-distortion performance.