Hybrid Video Signal Coding Technologies: Past, Current and Future

Video sequence generally contains a significant amount of statistical and perceptual redundancies. The ultimate goal of video coding is to reduce the average bits to represent the video signal by exploring these redundancies. Typically, the performance of video compression is related to both the amount of redundancy contained in the video data and the efficiency of the actual algorithms used for coding. With the substantially increase in high-quality video service, it requires more advanced techniques, and hencemany international video coding standards are developed in the past decades, including MPEG-2 Tudor (1995), H.264/Advanced Video Coding (AVC) Wiegand et al. (2003) and the latest High Efficiency Video Coding (HEVC) Sullivan et al. (2012). The standardization plays an important role in multimedia applications, which ensures interoperability and flexibility across a breadth of products made by different clients. To support communication across different platforms, the standards only define the syntax of the bitstream and describe the decodingmethod. Almost all the current standards are essentially block-based hybrid coding system, where video frame is split into non-overlapped blocks that are the basic coding unit. In a modern video system, spatial correlation and spectral correlations can be removed by predictive and transform coding, whereas temporal correlation can be removed by motion compensated prediction. As the cost for hardware has reduced and network support for coded video data has diversified, the need has arisen for video stream with higher resolution, higher frame rate, or higher bit-depth. If there are more pixels in each frame, more detailed information can be displayed. Ultra high-definition (UHD) television supports 4K (3840×2160) or 8K (7680×4320) resolutions, which are becoming popular at increasingly low prices. In addition, increasing the number of frames displayed can greatly improve the perceptual effect, especially for sportcastings and movies. At last, increasing the pixel bit width provides a more realistic scene, which can present the human eye with a comparable range of brightness and colors. Thus, how to efficiently compress the high-quality visual signal is the most fundamental driving force behind the development of next-generation video compression technology Zeng et al. (2013).