BACKGROUND

In some instances, constant bitrate (CBR) transport streams are sent between encoders and their statistical multiplexer (statmux) as opposed to a variable bitrate (VBR) transport stream. The difference between a CBR and VBR transport stream is that a CBR transport stream may include NULL packets to ensure the overall bitrate is constant. The constant bitrate can be measured by taking the timestamps between two consecutive program clock reference timestamps (PCRs) and dividing by the number of bits between them (such as by counting the number of MPEG Transport Stream (MTS) packets and multiplying by some number of bits per packet). Further, the PCR timestamp of any packet in a CBR transport stream can be inferred by finding the PCR of the preceding and next MTS packets and performing linear interpolation between them based on the number of packets between each. A VBR transport stream typically does not carry NULL packets and the bitrate calculation between pairs of PCRs as the values will not be the same.

