Hierarchical Coding of High Data Rate Video for Asynchronous Transfer Mode Networks

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High data rate video is an integral part of high-quality multimedia for broadband networks. Owing to the high rate, compression of video information is required for an efficient use of network bandwidth. A hierarchical DCT-based video codec is examined that prioritizes and compresses high data rate video for transmission over ATM networks.

The video codec utilizes intraframe coding by independently processing each frame of the video sequence. The lossless compression part consists of run length coding to exploit zero values in the high frequency DCT coefficients and variable length coding (VLC) to further reduce the bit rate. Three compression schemes are examined: adaptive Huffman, arithmetic coding, and Lempel-Ziv-Welch coding. For the model-based compression algorithms, we study several models to characterize the input bit stream to the VLC: memoryless, and Markov with either fixed orders or orders determined by an order estimator. For the three VLCs in the codec, the best performance was obtained from a combination of a memoryless Huffman codec and two first-order Huffman codecs. Many of the models incorporating memory, performed poorly due to the small size of the input files.

Due to the VLC, the output rate of the system is variable; however, since intraframe coding is utilized, rate variations are small. In order to fully utilize available bandwidth, we examine the rate control problem of converting the codec from a variable rate system to a fixed rate system. The rate control problem is formulated as one of constrained minimization, and analyzed for optimal solutions. Algorithms are presented for optimal rate control.