In this work, we improve the H.264 error resilient coding scheme in [1, 2] with a hybrid scheme that generates alternative SP macroblocks utilizing both multiple reference frames [1] and the concealed versions of corrupted frames [2]. The new scheme is more robust and able to work effectively under different coding environments. Although the bit rate overhead introduced by [1] and [2] is acceptable for some applications, we use an adaptive coding and bit stream replacement mechanism to reduce the overhead furthermore to meet the strict bandwidth constraints. Specifically, two different versions of alternative SP macroblocks are coded using different quantization levels. They provide different levels of error resilient performance with different bit rate consumptions. When the sender attempts to replace the originally coded version of a target macroblock in the bit stream, it will select one proper version according to the importance of the macroblock. The importance of the macroblock is measured by its influence to the subjective quality of the current frame and its impact to subsequent frames. The implementation and the standard conformance of the proposed scheme are detailed in this work.
A novel H.264 error resilient scheme aiming at stopping or reducing error propagation using the SP/SI coded macroblocks is proposed to maintain the quality of transmitted video through erroneous channels in this work. Specifically, for each encoded macroblock, we encode additional predicted versions using different reference frames (or different prediction methods) and save them as SP/SI macroblocks. During transmission, these SP/SI macroblocks are used to replace the originally coded macroblocks in the output video stream if they are affected by previous errors detected by the receiver. The way to encode these SP/SI macroblocks ensures that such a replacement will not cause any mismatch at the decoder side. It is confirmed by experimental results that the proposed scheme is effective in reducing error propagation so as to enhance the error resilient capability of H.264 video. This scheme introduces a small amount of overhead in the bit rate only when there are transmission errors, and does not have an overhead when no error occurs.
A multi-hypothesis motion compensated prediction (MHMCP) scheme, which predicts a block from a weighted superposition of more than one reference blocks in the frame buffer, is proposed and analyzed for error resilient visual communication in this research. By combining these reference blocks effectively, MHMCP can enhance the error resilient capability of compressed video as well as achieve a coding gain. In particular, we investigate the error propagation effect in the MHMCP coder and analyze the rate-distortion performance in terms of the hypothesis number and hypothesis coefficients. It is shown that MHMCP suppresses the short-term effect of error propagation more effectively than the intra refreshing scheme. Simulation results are given to confirm the analysis. Finally, several design principles for the MHMCP coder are derived based on the analytical and experimental results.
Multi-hypothesis motion compensated prediction (MHMCP) predicts a block from a weighted sum of multiple reference blocks in the frame buffer. By efficiently combining these reference blocks, MHMCP can provide less prediction errors so as to reduce the coding bit rates. Although MHMCP was originally proposed to achieve high coding efficiency, it has been observed recently that MHMCP can also enhance the error resilient property of compressed video. In this work, we investigate the error propagation effect in the MHMCP coder. More specifically, we study how the multi-hypothesis number as well as hypothesis coefficients influence the strength of propagating errors. Simulation results are given to confirm our analysis. Finally, several design principles for the MHMCP coder are derived based on our analysis and simulation results.
Multi-hypothesis motion compensated prediction (MHMCP) predicts a block from a weighted sum of multiple reference blocks in the frame buffer. By efficiently combining these reference blocks, MHMCP can provide less prediction errors so as to reduce the coding bit rates. Although MHMCP was originally proposed to achieve high coding efficiency, it has been observed recently that MHMCP can also enhance the error resilient property of compressed video. In this work, we investigate the error propagation effect in the MHMCP coder. More specifically, we study how the multi-hypothesis number as well as hypothesis coefficients influence the strength of propagating errors. Simulation results are given to confirm our analysis. Finally, several design principles for the MHMCP coder are derived based on our analysis and simulation results.
A dynamic mode-weighted error concealment method is proposed for video packets transmitted over noisy channels in this work. We first introduce two error concealment approaches. One is to reconstruct lost pixels by interpolating candidate pixels indicated by neighboring motion vectors. The other is to estimate the motion vector by a side matching algorithm. Four corrupted block reconstruction modes are described based on the two error concealment approaches. Then, the value of an erroneous pixel is replaced by a weighted sum of those reconstructed by two modes. The property of the weighted sum is analyzed. It is shown that the optimal weighting coefficients can be expressed as a formula in terms of the error variance and the correlation coefficients associated with the reconstruction modes. Furthermore, based on the decoder-based error tracking model, these weighting coefficients are dynamically updated to minimize the instant propagation and concealment error variance.
Extensive simulations are provided to demonstrate that the proposed method can lead to a satisfying performance in an error-prone environment.
A jointly designed source-channel coding technique that protects video signals against transmission errors is proposed in this work. We develop a low-complexity source model which can estimate the bitrate and the quantization error for each packet. Also, the channel distortion is estimated based on the packet importance and the packet loss rate. The packet importance is measured as the mean square error between the error-free reconstruction and the concealed reconstruction, and the packet loss rate is determined by channel conditions. According to the informed channel condition, the encoder adaptively assigns the quantization parameter and the channel code rate to each packet so that the expected mean square error due to source and channel distortions is minimized subject to a constraint on the overall bitrate. Simulation results show that the proposed adaptive system provides acceptable image quality even in a high bit error rate environment.
A robust video transmission technique that protects video signals over wireless channels is proposed in this work. First, we present new packetization and concealment methods for compressed video data. Second, the loss of each packet is quantitatively measured under this normative concealment method. More specifically, the encoder associates each packet with the mean square error between the error-free reconstruction and the concealed reconstruction. Third, a channel code rate is adaptively allocated to protect each packet so that the expected mean square error is minimized subject to a constraint on the overall bit rate. Extensive simulations show that the jointly designed video codec provides acceptable image quality in a high bit error rate environment. Besides, the proposed algorithm can be applied to real time video transmission applications, since its computational complexity is very low.
Effective transmission of multiple video signals over a CDMA system
simultaneously is investigated in this work. A channel code assignment
scheme that efficiently protects compressed bitstreams while minimizing
multiple access interference (MAI) is proposed. First, each video
signal is coded with a two-layer structure that consists of the base and
the enhanced bitstreams according to the bit importance. Then, these
bitstreams are protected against transmission errors with channel codes
such as RCPC. Better protection of higher bit-rate video requires more
multicodes in spreading, which can lead to a severe multiple access
interference problem. We set up a framework to a joint design of
channel codes and spreading codes with the feedback of the channel
status, and provide a solution to deal with the trade-off between
channel coding rates and the assigned number of multicodes to achieve
efficient transmission. Preliminary experimental results are presented
to demonstrate the performance of the proposed channel code assignment
scheme.
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