Algorithms for determining bitrate for a statistical multiplexing system to ensure stream alignment from encoders to the multiplexer
View Patent ↗A statistical multiplexer (statmux) system for encoding and multiplexing multiple channels of digital television data is provided that limits dropped bits due to misalignment of bit rate allocations to the encoders. Without such a system, if for example an encoder is allotted 0 bits during a first time period and 20 kilobits during a second time period, if the encoder jumps ahead from the first period to the second time period allocation, the 20 kilobits could be output during the 0 bit output allocation time period. This can cause buffer overflow downstream if other encoders are outputting at their maximum rate. To limit such misalignment, a maximum percentage increase of an encoder's bitrate allocation is set from time period to time period based on a formula to prevent bits from being dropped when misalignment occurs.
1. A method for allocating bits in a statistical multiplexer comprising:
allocating a first bit rate allowed for the output of each of a plurality of encoders supplying a multiplexer during a first time period;
determining a bit rate increase from the first bit rate for each of the encoders; and
allocating a second bit rate allowable to each of the encoders for a second time period, subsequent to the first time period, wherein the second bit rate is limited by the determined bit rate increase,
wherein misalignment of application of the second bit rate to a given one of the encoders can cause the second bit rate output to be provided in the first time period by the given encoder, and
wherein the bit rate increase is determined so that when the misalignment of the second bit rate can occur for the second bit rate to be output in the first time period, the bit rate increase is set so that a total number of bits processed by the given encoder using the second rate does not exceed the encoder capacity that will cause bits to be dropped by the multiplexer.
2. The method of claim 1 , wherein the bit rate increase is a percentage of the first bit rate.
3. The method of claim 1 , wherein the bit rate increase is applied when inverse telecine frames are being processed.
4. The method of claim 1 , wherein the first time period and the second time period are defined by a number of sample periods, and the bit rate increase is defined by a size of one of the sample periods and a size of a packet buffer providing bits to the multiplexer.
5. The method of claim 1 , wherein the bit rate increase is further defined by a predetermined maximum allowable alignment error.
6. A statistical multiplexing system comprising:
encoders for coding a plurality of channels of video data sources;
a multiplexer for receiving the output of the encoders and providing from the output of the encoders a single data stream; and
a statistical multiplexer (statmux) controller for receiving need parameter data from the encoders and for providing to the encoders bit rate data based on the need parameter data, the statmux controller including a memory storing code to enable the statmux controller to:
allocate a first bit rate allowed for the output of each of the encoders supplying the multiplexer during a first time period;
determining a bit rate increase from the first bit rate for each of the encoders; and
allocating a second bit rate allowable to each of the encoders for a second time period, subsequent to the first time period, wherein the second bit rate is limited by the determined bit rate increase,
wherein misalignment of application of the second bit rate to a given one of the encoders can cause the second bit rate output to be provided in the first time period by the given encoder, and
wherein the bit rate increase is determined so that when the misalignment of the second bit rate can occur for the given encoder to cause the second bit rate to be output in the first time period, the bit rate increase is set so that a total number of bits processed by the given encoder using the second rate does not exceed the encoder capacity that will cause bits to be dropped by the multiplexer.
7. The statistical multiplexing system of claim 6 , wherein the bit rate increase is a percentage of the first bit rate.
8. The statistical multiplexing system of claim 6 , wherein the bit rate increase is applied when inverse telecine frames are being processed.
9. The statistical multiplexing system of claim 6 , wherein the first time period and the second time period are defined by a number of sample periods, and the bit rate increase is defined by a size of one of the sample periods and a size of a packet buffer providing bits to the multiplexer.
10. The statistical multiplexing system of claim 6 , wherein the bit rate increase is further defined by a predetermined maximum allowable alignment error.
11. A non-transitory computer readable medium containing an executable program to enable a controller in of a statistical multiplexer (statmux) system that provides a bit rate signal to a plurality of encoders in the statmux system, the program causing controller to:
allocate a first bit rate allowed for the output of each of a plurality of encoders supplying a multiplexer during a first time period;
determine a bit rate increase from the first bit rate for each of the encoders; and
allocate a second bit rate allowable to each of the encoders for a second time period, subsequent to the first time period, wherein the second bit rate is limited by the determined bit rate increase,
wherein misalignment of application of the second bit rate to a given one of the encoders can cause the second bit rate output to be provided in the first time period by the given encoder, and
wherein the bit rate increase is determined so that when the misalignment of the second bit rate can occur for the given encoder to cause the second bit rate to be output in the first time period, the bit rate increase is set so that a total number of bits processed by the given encoder using the second rate does not exceed the encoder capacity that will cause bits to be dropped by the multiplexer.
12. The non-transitory computer readable medium of claim 11 , wherein the first time period and the second time period are defined by a number of sample periods, and the bit rate increase is defined based on a size of one of the first and second sample periods.
13. The non-transitory computer readable medium of claim 11 , wherein the bit rate increase is further defined by a predetermined maximum allowable alignment error.