Abstract-A theoretical analysis of the overall mean squared error (MSE) in hybrid video coding is presented for the case of error prone transmission. Our model covers the complete transmission system including the rate-distortion performance of the video encoder, forward error correction, interleaving, and the effect of error concealment and interframe error propagation at the video decoder. The channel model used is a 2-state Markov model describing burst errors on the symbol level. Reed-Solomon codes are used for forward error correction. Extensive simulation results using an H.263 video codec are provided for verification. Using the model, the optimal tradeoff between INTRA and INTER coding as well as the optimal channel code rate can be determined for given channel parameters by minimizing the expected MSE at the decoder. The main focus of this paper is to show the accuracy of the derived analytical model and its applicability to the analysis and optimization of an entire video transmission system. Index Terms-Error resilience, intra-update, joint sourcechannel coding, robust video transmission, tradeoff sourcechannel coding, video transmission system model.

No abstract

Abstract-A new receiver-based playout scheduling scheme is proposed to improve the trade-off between buffering delay and late loss for real-time voice communication over IP networks. The scheme estimates the network delay from past statistics and adaptively adjusts the playout time of the voice packets. In contrast to previous work, the adjustment is not only performed between talkspurts, but also within talkspurts in a highly dynamic way. Proper reconstruction of continuous playout speech is achieved by scaling individual voice packets using a time-scale modification technique based on the WSOLA algorithm. Results of subjective listening tests show that this operation does not impair audio quality, since the adaptation process requires infrequent scaling of the voice packets and low playout jitter is perceptually tolerable. The same time-scale modification technique is also used to conceal packet loss at very low delay, i.e., one packet time. Simulation results based on Internet measurements show that the trade-off between buffering delay and late loss can be improved significantly. The overall audio quality is investigated based on subjective listening tests, showing typical gains of 1 on a 5-point MOS scale.

No abstract

| In this paper we address the problem of robust video transmission in error prone environments. The approach is compatible with the ITU-T video coding standard H.263. Fading situations in mobile networks are tolerated and the image quality degradation due to spatio-temporal error propagation is minimized utilizing a feedback channel between transmitter and receiver carrying acknowledgment information. In a rst step, corrupted Group of Blocks (GOBs) are concealed to avoid annoying artifacts caused by decoding of an erroneous bit stream. The GOB and the corresponding frame number are reported to the transmitter via the back channel. The encoder evaluates the negative acknowledgments and reconstructs the spatial and temporal error propagation. A low complexity algorithm for real-time reconstruction of spatio-temporal error propagation is described in detail. Rapid error recovery is achieved by INTRA refreshing image regions (Macroblocks) bearing visible distortion. The feedback channel method does not introduce additional delay and is particularly relevant for real-time conversational services in mobile networks. Experimental results with bursty bit error sequences simulating a DECT channel are presented with di erent combinations of Forward Error Correction (FEC), Automatic Repeat on Request (ARQ), and the proposed error compensation technique. Compared to the case where FEC and ARQ are used for error correction, a gain of up to 3 dB Peak Signal to Noise Ratio (PSNR) is observed if error compensation is employed additionally. Keywords| Error Tracking, mobile video communication, H. 263.