# Block Recovery Rate-Based Unequal Error Protection for Three-Screen TV
## 1 Introduction  
Recently, various multimedia services over wireless and wired networks using video streaming technologies have been emerging [1]. In particular, both continuous packet losses and rapid bandwidth changes in a time-varying wireless environment lead to serious video quality degradation. This paper proposes an unequal error protection (UEP) algorithm of scalable video to minimize video quality degradation caused by the packet losses over time-varying wireless channels.  
Scalable video is an efficient encoder which can provide spatial, temporal, and quality scalabilities without any additional computations [2, 3]. The characteristic of scalable video allows one single scalable bitstream to provide different video quality and resolution to different video receivers. Depending on channel characteristics or decoding capability of the receiver, it is possible to transmit, as well as decode, the partial or whole bitstreams of scalable video from the server, the intermediate node between the server and the receiver. Although the scalable embedded bitstream can easily adapt to various network environments, the packet losses in unstable channel conditions can cause serious video quality degradation in the compressed bitstream due to the strong spatio-temporal dependencies between scalable video layers. Since the structure of scalable video compression has strong spatial and temporal dependencies, the packet losses in hierarchical coding structures with scalability can substantially deteriorate the received video quality. Thus, considering both the hierarchical coding structure and the dependencies between quality layers, the effect on overall video quality degradation from packet losses in each layer is utilized as weighting in various UEP algorithms.  
Figure 1 depicts the conceptual diagram of a three-screen TV using scalable video coding (SVC) with high-definition TV (HDTV), standard-definition TV (SDTV), and low-definition TV (LDTV) (such as mobile device). A traditional solution for source coding is to prepare multiple pre-encoded video files (chunks) according to the performance capability of each targeted device: such as screen resolution, computational power, and available network bandwidth. Due to the multiple redundancies, the video streaming server requires relatively large storage as well as a significant bandwidth adaptation problem in wireless error-prone networks.  
There is another solution using transcoding with down sampling. By transcoding one high resolution and high bit rate video sequence for targeted screen resolution and bandwidth of TV clients, a video service provider (VSP) can reduce storage redundancies as well as adapt to bandwidth fluctuations. However, this solution requires too much computing power to support multiple TVs that have variable screen resolutions at the same time. Thus, it is very hard to apply in a real-time video streaming system.  
This paper proposes a new video streaming solution for a three-screen TV that has low computational complexity and error robustness. First, it proposes the combined source and channel coding technologies: (1) application-level unequal error protection (UEP) technology for recovering packet losses over error-prone networks; (2) SVC-based adaptive layer-switching method that enables the server to select best scalable layers of SVC network abstraction layer (NAL) bitstreams according to the available bandwidth.  
This paper is organized as follows: Section 2 gives an overview of the H.264 SVC, H.265 SHVC, and channel coding with Raptor forward error correction (FEC) codes. Section 3 proposes a new UEP algorithm to minimize the video quality degradation from packet losses, and an adaptive SVC layer switching method with Raptor FEC overhead adaptation. Section 4 presents the system design and implementation while also verifying the performance of proposed system. Finally, Section 5 provides conclusions.