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Abstract

Four QCIF video input signals generated by participants in a multiparty video conference are combined in the coded domain to produce a merged CIF video output signal. When the CIF video output signal is transmitted back to each party's video terminal, a combined 2.times.2 image is displayed. A video signal combiner (700) combines the input video signals in the coded domain by time-division multiplexing the inputs at the GOB level. In order to maintain frame synchronization between the inputs which may be arriving at different frame repetition rates, the combiner stores the inputs in buffers (706-709) and processes (710) the temporal reference (TR) numbers associated with each frame in each input before merging the GOBs from each input in accordance with the processed TR number. Specifically, the TR of each input is offset by an initial TR number associated with each input and determined at turn-on. The offset TR in each input is then mapped onto a scale of TR numbers that is common to each input. The each output frame is formed by time-division multiplexing GOBs from the inputs that have the same offset and mapped TR number. Only GOB headers and empty data fields are inserted into the combined data stream for those inputs not having a frame with that same mapped TR number.

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First Claim