Apparatus and method for multiplexing with small buffer depth

DETAILED DESCRIPTION It is known that the delay introduced by a multiplexing system increases when buffer sizes or depth increases.
Therefore, a multiplexing method that introduces minimum delay is desirable.
According to the present invention, an optimal multiplexing method is provided which allows buffers to be two packets in depth.
Accordingly, for a plurality of buffers, each buffer associated with a packetized input data stream and having a buffer depth, packets are received at respective buffer input rates.
The packetized input data streams are, for example, MPEG transport streams.
The buffers are serviced at a service rate at least equal to a sum of the buffer input rates to provide an output data stream.
At least one null packet is sent until at least one of the buffers has received a full packet.
For each buffer, once a full packet has been received therein, a time interval until that buffer is expected to reach its buffer depth is determined.
The buffer having the least time interval is then serviced first, such that overflow of the buffers is avoided.
If more than one buffer has the least time interval, then that buffer having the fastest buffer input rate is serviced first.
While the preferred embodiments are described with reference to MPEG-2 Systems standard Transport Streams, the principles of the present invention are intended to encompass the multiplexing of any data streams that comprise fixed length packets and have a self-contained directory structure which describes the multiplex.
Thus, while the term "transport stream" is used herein to denote a Transport Stream as defined by the MPEG-2 Systems standard, the principles of the present invention are also applicable to systems using similar transport structures such as Asynchronous Transfer Mode (ATM) systems.