Margaret H. Pinson and Stephen Wolf

Abstract: This contribution presents new techniques for estimating temporal delays between input and output video streams from video teleconferencing systems. The discussion in this contribution considers "variable alignment," defined as an alignment process that can assign a unique alignment offset, or delay, to every output video frame in a given output video sequence. To achieve the bandwidth reduction necessary for in-service measurements, the variable alignment techniques presented in this contribution are applied to subsampled video images. We have found that a sub-sampling factor of 128 to 1 produces useful variable alignment results. Regardless of the sub-sampling factor used (including sub-sampling factors of 1), there is always a possibility of misalignment. The probability of misalignment increases as the amount of scene motion decreases and the video distortion present in the output increases. Therefore, it has been necessary to implement artificial intelligence techniques that examine the set of most probable alignments produced by the signal processing portion of the algorithm. All of the techniques presented in this contribution can also be applied to whole field correlation algorithms such as those given in ANSI T1.801.04.

Keywords: video delay; temporal alignment; medium bandwidth features

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