11. Media Synchronization in Networked Multisensory Applications with Haptics

In this chapter, we explain the present status of studies for media synchronization in networked multisensory applications with haptics. We also specify the characteristics of haptic media and different features of haptic media from other media such as olfactory, auditory, and visual media. By using such other media together with haptic media, we can get higher realistic sensation when we use the applications for various purposes such as remote education, entertainment, and networked games. When multisensory media streams are transmitted over a network like the Internet, the temporal relationships among the media streams may be disturbed owing to the network delay, delay jitter, and packet loss. Thus, the quality of experience (QoE) may seriously be degraded. To solve this problem, we need to carry out media synchronization control. To achieve a high quality of media synchronization, a number of media synchronization algorithms have been proposed so far. Especially, in networked multisensory applications, we need to take account of human perception of media synchronization errors in the algorithms. This is because the requirements of media synchronization quality depend on types of media. Some algorithms such as Virtual-Time Rendering (VTR) take human perception of the errors into account. For example, VTR tries to accomplish the synchronization by changing the buffering time of each media stream dynamically according to the network delay jitter with several threshold values about the errors. In the algorithms, instead of synchronizing the output timings of media streams exactly, ranges of human perception such as the allowable range, in which users feel that the synchronization error is allowable, the imperceptible range, in which users cannot perceive the error, and the operation range, which is narrower than the imperceptible range and should be kept usually, are taken into account for the sake of high synchronization quality. In this chapter, we explain the algorithms taking account of human perception of the media synchronization errors and enhance other algorithms such as the group (or inter-destination) synchronization control and the adaptive ∆-causality control algorithms for simultaneous output-timing control among multiple terminals by taking account of the perception. It is indispensable to clarify the ranges by QoE assessment in networked multisensory applications. In this chapter, we further make a survey of studies on the assessment. Finally, we discuss the future directions of media synchronization in networked multisensory applications with haptics.