Real Video Content Research Articles

ASAP

The dramatic growth of video traffic represents a practical challenge for cellular network operators in providing a consistent streaming Quality of Experience (QoE) to their users. Satisfying this objective has so-far proved elusive, due to the inherent characteristics of wireless networks and varying channel conditions as well as variability in the video bitrate that can degrade streaming performance. In this article, we propose stall-aware pacing as a novel MPEG DASH video traffic management solution that reduces playback stalls and seeks to maintain a consistent QoE for cellular users, even those with diverse channel conditions. These goals are achieved by leveraging both network and client state information to optimize the pacing of individual video flows. We evaluate the performance of two versions of stall-aware pacing techniques extensively, including stall-aware pacing (SAP) and adaptive stall-aware pacing (ASAP), using real video content and clients, operating over a simulated LTE network. We implement state-of-the-art client adaptation and traffic management strategies for direct comparisons with SAP and ASAP. Our results, using a heavily loaded base station, show that SAP reduces the number of stalls and the average stall duration per session by up to 95%. Additionally, SAP ensures that clients with good channel conditions do not dominate available wireless resources, evidenced by a reduction of up to 40% in the standard deviation of the QoE metric across clients. We also show that ASAP achieves additional performance gains by adaptively pacing video streams based on the application buffer state.

The visibility of color breakup and a means to reduce it.

Color breakup is an artifact seen on displays that present colors sequentially. When the eye tracks a moving object on such a display, different colors land on different places on the retina, and this gives rise to visible color fringes at the object's leading and trailing edges. Interestingly, color breakup is also observed when the eye is stationary and an object moves by. Using a novel psychophysical procedure, we measured breakup both when viewers tracked and did not track a moving object. Breakup was somewhat more visible in the tracking than in the non-tracking condition. The video frames contained three subframes, one each for red, green, and blue. We spatially offset the green and blue stimuli in the second and third subframes, respectively, to find the values that minimized breakup. In the tracking and non-tracking conditions, spatial offsets of Δx/3 in the second subframe (where Δx is the displacement of the object in one frame) and 2Δx/3 in the third eliminated breakup. Thus, this method offers a way to minimize or even eliminate breakup whether the viewer is tracking or not. We suggest ways to implement the method with real video content. We also developed a color-breakup model based on spatiotemporal filtering in color-opponent pathways in early vision. We found close agreement between the model's predictions and the experimental results. The model can be used to predict breakup for a wide variety of conditions.

H.264/SVC 공간 계위 부호화 기반 지상파 다채널 하이브리드 고화질 방송 서비스 프레임워크 및 H.264/SVC 부호화 성능 평가

기존의 다채널 지상파 디지털 TV 서비스인 KoreaView는 6MHz의 대역폭을 유지하면서 1개의 MPEG-2기반 HD 비디오와 3개의 H.264/AVC기반 SD 비디오, 총 4개의 채널을 제공하는 서비스이다. 그러나 KoreaView는 추가되는 3개의 SD급 비디오 채널이 작은 공간 해상도와 낮은 목표 비트율로 인한 화질 열화 때문에 높은 시청 만족도를 제공하지 못하는 단점을 가지고 있다. 본 논문에서는 이러한 KoreaView의 한계점을 극복하기 위한 공간 계위 스케일러블 비디오 부호화 기반 지상파 다채널 하이브리드 고화질 방송 서비스 프레임워크를 제안한다. 제안하는 지상파 다채널 하이브리드 고화질 방송 서비스 프레임워크는 H.264/AVC 기반 SD 비디오 3개를 H.264/SVC 공간 기본 계층 부호화를 통해 동일하게 서비스 하고, 공간 향상 계층 부호화로 추가된 3개의 HD 비디오를 광대역망을 통해 전송하여 고화질의 다채널 방송을 서비스를 가능하게 한다. 이같이 기존의 3개의 SD 채널에 공간 향상 계층을 추가적으로 전송하면 고화질 채널을 통해 높은 시청 만족도를 갖는 여러 개의 채널을 확보하게 된다. 제안하는 프레임워크의 성능을 검증하기 위하여 실제로 방송에서 사용되는 다양한 영상을 이용하여 실험을 수행하였다. 먼저 H.264/SVC를 이용하여 SD 입력 비디오가 공간 기본 계층에서 1.5Mbps 목표 비트율로 부호화될 때, 34.5-42.9dB의 화질을 제공하여 상용 서비스가 가능한 수준의 객관적 화질을 제공 할 수 있음을 확인할 수 있었다. 또한 12Mbps 목표 비트율로 부호화된 MPEG-2 기반 HD 복원 영상과 제안하는 서비스 프레임워크의 H.264/SVC 공간 향상 계층의 HD 복원 영상을 비교하여 부호화 성능을 분석하였다. MPEG-2 기반 HD 복원 영상과 유사한 객관적 화질 수준을 제공하기 위하여 제안하는 서비스 프레임워크에서 사용된 H.264/SVC 공간 계위 부호화를 수행한 결과 실험 영상의 종류와 특성에 따라 약 690kbps에서 8,200kbps의 비트율이 발생함을 실험을 통하여 확인하였다. One of the existing terrestrial multi-channel DTV service frameworks, called KoreaView, provides four programs, composed of MPEG-2 based one HD video and H.264/AVC based three SD videos within one single 6MHz frequency bandwidth. However the additional 3 SD videos can not provide enough quality due to its reduced spatial resolution and low target bitrates. In this paper, we propose a framework, which is called a terrestrial multi-channel high quality hybrid DTV service, to overcome such a weakness of KoreaView services. In the proposed framework, the three additional SD videos are encoded based on an H.264/SVC Spatial Base layer, which is compliant with H.264/AVC, and are delivered via broadcasting networks. On the other hand, and the corresponding three additional HD videos are encoded based on an H.264/SVC Spatial Enhancement layer, which are transmitted over broadband networks such as Internet, thus allowing the three additional videos for users with better quality of experience. In order to verify the effectiveness of the proposed framework, various experimental results are provided for real video contents being used for DTV services. First, the experimental results show that, when the SD sequences are encoded by the H.264/SVC Spatial Base layer at a target bitrate of 1.5Mbps, the resulting PSNR values are ranged from 34.5dB to 42.9dB, which is a sufficient level of service quality. Also it is noted that 690kbps-8,200kbps are needed for the HD test sequences when they are encoded in the H.264/SVC Spatial Enhancement layer at similar PSNR values for the same HD sequences encoded by MPEG-2 at a target bitrate of 12 Mbps.