Described herein are systems, methods and apparatus for demultiplexing and multiplexing multimedia streams where one or more of the underlying elementary streams appears intermittently, that is, one or more particular elementary streams are “spurious”. Typically, a multiplexed multimedia stream contains elementary streams for video, audio and ancillary data. A transcoding process typically involves demultiplexing into elementary streams, transcoding, and then multiplexing the elementary streams back into a multiplexed stream. Bu if one of the elementary streams is not present for a time period, then a multiplexer that expects a continuous stream of data of each elementary stream type may fail or excessively buffer the elementary streams that are present. Without limitation, the teachings presented here provide solutions to the problems of handling spuriously appearing sources in a transcoding solution.