VBR Transport Stream

[Mobileace]

If i encode my mpeg-2 elementary stream as a VBR Mpeg-2 video, after multiplexing it as a tranport stream, can i get a varaible bitrate TS? or is it back to constant bitrate TS? Anyone have any idea?

[Guest]

I'll tell you my own experience. Transport rates are fixed at the time of multiplexing. If you have a good multiplexer, it will pad out the stream to keep the fixed transport rate. This is what the Hewlett Packard MPEGScope and Tektronix MTS systems do that we have here where I work. Obviously, the transport rate must be high enough to accommodate peak rates of the streams being multiplexed. The video stream itself remains VBR after being demultiplexed by the receiver.

[Mobileace]

ohhh.. does that meant that when the peak bitrate is not used.. the rest of the bits will become null packets? So theoritically, i should have a variable null packets bitrate right?Correct me if i am wrong!!!

[Guest]

When the instantaneous sum of the audio, video, etc., data rates is less than the fixed transport rate, then padding is added to reach the required fixed transport rate. So, yes you will have a variable null packet rate if the streams are VBR.