Demultiplexing a statistically multiplexed MPEG transport stream into CBR single program transport streams
View Patent ↗A constant bit rate single program encoded transport stream is demultiplexed from a statistically multiplexed MPEG transport stream by separating a variable bit rate program from the multiplexed MPEG transport stream, loading the sequence of pictures that form the variable bit rate program into a smoothing buffer at a rate that does not exceed a desired constant bit rate and transferring the picture from the smoothing buffer at times indicated by decode time stamps associated with the pictures respectively. If a picture of the sequence becomes available no later than a specified amount of time prior to the picture's decode time stamp, then that picture is loaded into the smoothing buffer commencing the specified amount of time prior to the time indicated by the picture's decode time stamp. If a picture of the sequence becomes available later than the specified amount of time prior to the picture's decode time stamp, then that picture is loaded into the smoothing buffer as soon as possible.
1. A method of demultiplexing a statistically multiplexed MPEG transport stream into a constant bit rate single program transport stream comprising the steps of:
separating a specified single program transport stream including a variable bit rate program composed of a sequence of pictures, each picture having a decode time stamp, from the statistically multiplexed MPEG transport stream;
loading a j'th picture from the variable bit rate program into a smoothing buffer at a desired constant bit rate,
in the event that loading of the j'th picture into the smoothing buffer is completed no later than a time δ before the time indicated by the decode time stamp of the (j+1)'th picture, loading the (j+1)'th picture into the smoothing buffer at said desired constant bit rate starting at the time δ before the time indicated by the decode time stamp of the (j+1)'th picture,
in the event that loading of the j'th picture into the smoothing buffer is not completed until later than the time δ before the time indicated by the decode time stamp of the (j+1)'th picture, loading the (j+1)'th picture into the smoothing buffer at said desired constant bit rate starting substantially immediately after loading of the j'th picture is completed, and
transferring the (j+1)'th picture from the smoothing buffer at the time indicated by the decode time stamp of the (j+1)'th picture.
2. A method according to claim 1 , wherein the smoothing buffer has a capacity equal to said desired constant bit rate multiplied by δ.
3. A method of adjusting bit rate of a variable bit rate single program transport stream having an average bit rate less than a desired constant bit rate and having a maximum bit rate greater than said desired constant bit rate, the single program transport stream being composed of a sequence of pictures each having a decode time stamp, the method comprising the steps of:
(a) loading a j'th picture of the sequence into a smoothing buffer,
(b) transferring the j'th picture from the smoothing buffer for decoding,
(c)(1) in the event that loading of the j'th picture into the smoothing buffer is completed no later than a time δ before the time indicated by the decode time stamp of the (j+1)'th picture, loading the (j+1)'th picture into the smoothing buffer at said desired constant bit rate starting at the time δ before the time indicated by the decode time stamp of the (j+1)'th picture,
(c)(2) in the event that loading of the j'th picture into the smoothing buffer is not completed until later than the time δ before the time indicated by the decode time stamp of the (j+1)'th picture, loading the (j+1)'th picture into the smoothing buffer at said desired constant bit rate starting substantially immediately after loading of the j'th picture is completed, and
(d) transferring the (j+1)'th picture from the smoothing buffer at the time indicated by the decode time stamp of the (j+1)'th picture.
4. A method according to claim 3 , wherein the single program transport stream is one stream of a statistically multiplexed MPEG transport stream having a plurality of variable bit rate single program streams multiplexed together and each composed of a sequence of pictures each having a decode time stamp, and the method comprises, before step (a):
providing a plurality of smoothing buffers for said plurality of single program transport streams respectively, and
separating said single program transport streams from the statistically multiplexed MPEG transport stream,
and step (a) comprises, for each single program transport stream, loading the j'th picture from the variable bit rate program into the smoothing buffer provided for that single program transport stream.
5. A method according to claim 4 , wherein step (c)(1) comprises, for each single program transport stream, in the event that loading of the j'th picture of the single program transport stream into the smoothing buffer provided for that single program transport stream is completed no later than a time δ before the time indicated by the decode time stamp of the (j+1)'th picture, loading the (j+1)'th picture of the single program transport stream into the smoothing buffer provided for that single program transport stream at said desired constant bit rate starting at the time δ before the time indicated by the decode time stamp of the (j+1)'th picture.
6. A method according to claim 5 , wherein step (c)(2) comprises, for each single program transport stream, in the event that loading of the j'th picture of the single program transport stream into the smoothing buffer provided for that single program transport stream is not completed until later than the time δ before the time indicated by the decode time stamp of the (j+1)'th picture, loading the (j+1)'th picture of the single program transport stream into the smoothing buffer provided for that single program transport stream at said desired constant bit rate starting substantially immediately after loading of the j'th picture is completed.