Researches On Key Issues Of Video Communication Based On H.263

Video transmission over unreliable channels such as wireless channels and Internet has become trend of video communication. However, there are some inherent problems in wireless channels and Internet that affect video delivery, such as limited bandvvidth, varying delay and high levels of noise. Some key issues in video transmission based on H.263, including video compression, error resilient and video quality evaluation are studied in this paper. Finally, a video transmission DEMO in LAN is implemented.When a video stream is conveyed through a vvireless channel or Internet to the receiver end, it is exposed to high levels of bit errors or packet loss. These errors severely degrade the service quality of video communication due to the propagation and accumulation of errors throughout the transmitted video stream. There are several procedures used to reduce these deteriorating effects, including the use of Forward Error Correction techniques, error concealment methods and error resilience schemes.This paper studies error resilient techniques in Internet video transmission. In this techeniques, Reed-Solomon(RS) codes across packets is used for error protection against packet loss, and a self-adaptive error concealment method based on motion feature is proposed, which can conceal errors more effectively, particularly for video sequences with acute motion.Due to limited bandvvidth and stringent requirements of real-time video plavback, video coding is an indispensable process for many visual communication applications and always requires a very high compression ratio. Generally speaking, a coding algorithm must be low complexity and work at high speed. In this paper, the coding methods are studied to increase coding speed. Firstly, a novel method based on temporal prediction to detect all-zero DCT coefficients is proposed, which can greatly reduce the coding cost and maintain a good tradeoff between correct detecting ratio and false detecting ratio with little additional computation. Secondly, a new diamond search (DS) algorithm for fast block-matching motion estimation is implemented. We also map some of the instructions onto IntePs MMX architecture. Using the above algorithms, H.263 baseline video-encoder implementation can encode more than 40fps in QCIF resolution on a Pentium MMX 500-MHz computer.Almost ali of the low bit-rate video compression techniques degrade quality. To combine the video quality evaluation with HVS, the relationship betvveen the motion activity and perceptual video quality are studied, and a video quality evaluation method based on motion activity is proposed, in which video defmition and smoothness are defined.Finally, a near real-time software-only DEMO is presented to demonstrate the overall procedure from video acquirement, video coding, transmission, to video decoding and playing, which confirm the practicability and efficiency of above techeniques.