DIGITAL TELEVISION SCANNING
|Statistic Multiplexing (VBR/CBR)|
The goal of this webpage is to explain the Statistic multiplexing (Variable bit rate) versus the constant bitrate.
1) Fin the max bitrate of the mux :
2) Number of services boradcasted in this mux:
3) Video bitrate measurment of each Tv channel at the same time:
4) All bitrates linked in one mux:
We can see that the summing of all video bitrates is around 22Mb/s. France2 during it's breaking news tv show has it's bitrate decreasing, other channels are taking this bitrate availabilty for their proper use.
France3 stays at constant bitrate. It was done to allow switch for other France3 with same bitrate in each area (local channels).
In CBR (Constant Bit rate), the bitrate needs to be the max allowed to the channel. 6Mb/s in MPEG2 CBR is a good broadcast. If more is allowed, the number of channels in a mux has to be decreased.
Today, a lot of provider are using statistic multiplexing in MPEG2 and MPEG4.
When CBR is used, it is due to the fact that all channels are compressed in an other place than the link of transport stream. This do not allow 2 steps compression and bitrate comparison.