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We study and analyze the computational complexity of a software-based H.264/AVC (advanced video codec) baseline profile decoder. Our analysis is based on determining the number of basic computational operations required by a decoder to perform the key decoding subfunctions. The frequency of use of each of the required decoding subfunctions is empirically derived using bitstreams generated from two different encoders for a variety of content, resolutions and bit rates. Using the measured frequencies, estimates of the decoder time complexity for various hardware platforms can be determined. A detailed example is provided to assist in deriving time complexity estimates. We compare the resulting estimates to numbers measured for an optimized decoder on the Pentium 3 hardware platform. We then use those numbers to evaluate the dependence of the time complexity of each of the major decoder subfunctions on encoder characteristics, content, resolution and bit rate. Finally, we compare an H.264/AVC-compliant baseline decoder to a decoder that is compliant with the H.263 standard, which is currently dominant in interactive video applications. Both "C" only decoder implementations were compared on a Pentium 3 hardware platform. Our results indicate that an H.264/AVC baseline decoder is approximately 2.5 times more time complex than an H.263 baseline decoder.