ANSI-ISO-IEC-13818-9-1996-R2007.pdf
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1、INTERNATIONAL STANDARD ISO/IEC 13818-g First edition 1996-l 2-l 5 Information technology - Generic coding of moving pictures and associated audio information - Part 9: Extension for real time interface for systems decoders Technologies de /information - Codage g. l real-time constraints are imposed
2、on the values of PCR in relation to their arrival time in the RTD; l the buffer sizes defined in the T-STD are different in the RTD; and l there is an extra requirement on the Transport Buffer occupancy (see the end of 2.4). 2.2 Clock Frequency Requirements The requirements on the system clock with
3、respect to frequency and frequency slew given in ISO/IEC 138 18-1,2.4.2.1 are also mandatory for the Real-Time Interface. 2.3 PCR Accuracy Requirements This subclause defines a single constraint on the relationship between the arrival time of all the bytes containing the last bit of a program-clock-
4、reference-base field for a single program of a Transport Stream, and the value carried in the corresponding program clock references. Specifically, l let system-clock-counter(t) be a counter that counts cycles of a system clock that satisfies the frequency requirements specified in 2.2 above, where
5、t represents time; l let i” be the index of a byte containing the last bit of a program-clock-reference-base field; l let t(i”) be the time at which byte i” arrives in the RTD; and l let PCR(i”) be the value of the program clock reference associated with byte i”; then there shall exist such a system
6、 clock-counter(t), a sequence of times e(i”), and a constant tjitter (see ISO/IEC 13 8 18- 1 Annex J) that satisfy PCR(i”) = system-clock-counter(t(i”) + e(i”)%(300 x 233), and - tjitterl:! I e(F) I tjitter/2. 2.4 Buffer Requirements The buffers in the RTD have the same names as those in the T-STD,
7、but are denoted with a “-r” suffix. Their sizes are: TBS-r, = TBS, + (tjitter x Rx”) + 188 bytes TB Srrsys = TBS, + ( tjitter x Rxn) + 188 bytes sb-size-r = sb-size + ( tjitter x sb-leak-rate) + 188 bytes It should be noted that the use of the smoothing buffer (see ISO/IEC 138 18-l) 2.6.30) is optio
8、nal for this part of ISO/IEC 13818, as it is in ISO/IEC 13818-1. 2 Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 07/16/2007 01:30:23 MDTNo reproduction or networking permitted without licen
9、se from IHS -,-,- 0 ISO/I EC ISO/IEC 13818-9:1996(E) The multiplex buffer (for video) and the decoder buffer (for audio and systems data) in the RTD have the sizes: MBS-r, = MBS, + (2x tjitter X Rx,), BS-r, = BS, + (2 x tjitter x Rxn), and BS-r, = BS, + (2 x tjitter X Rx,), respectively. Note that i
10、n all these equations, Rx, which is identical in definition to the same variable in the T-STD, is expressed in bytes/second for convenience. Given the RTD buffers as defined above, and a system clock that fulfils the above requirements, the RTD imposes that all the buffer constraints imposed by the
11、T-STD in ISO/IEC 138 18- 1 be complied with. In addition, the buffer state of the buffer TB-r, in the RTD at the arrival of the first byte of any Transport Stream packet shall be no more than the size of that buffer minus 188 bytes. 2.5 Real-Time Interface for Low Jitter Applications This subclause
12、specifies the Real-Time Interface for Low Jitter Applications (RTI-LJ). For a bitstream and its byte delivery schedule to comply with the RTI-LJ, they must obey all of the compliance tests in clause 3 below with tjitter equal to 50 microseconds. For a decoder to comply with the RTI-LJ, the decoder s
13、hall be capable of operating correctly when fed by any such bitstream and byte delivery schedule. 2.6 Other Applications Applications other than those described in 2.5 may use this part of ISO/IEC 13818 to specify interoperability constraints on bitstream delivery and bitstream decoders. In such usa
14、ge, compliance with this part of ISO/IEC 13 8 18 shall be stated relative to a specified value for tjitter. For example, a decoder may be called “RTI-compliant for tjitter equals x”. 3 Compliance Testing for RTI 3.1 Objectives The objectives of a testing procedure for this part of ISO/IEC 138 18 are
15、 the following: 1. Test for compliance with the system clock frequency accuracy specification, 2. Test for compliance with the system clock slew rate specification, 3. Test for compliance with the PCR jitter specification in this part (tjitter), and 4. Test for compliance with the buffer requirement
16、s in this part. For some Transport Streams, e.g. very short streams or streams with frequent PCR discontinuities, it may be impossible to verify all of these requirements. In streams with many closely spaced PCR discontinuities it is not possible to distinguish between system clock inaccuracy and ji
17、tter. Streams need to have a minimum duration of continuous PCRs for accurate determination of system clock frequency error. The duration of continuous PCRs must be sufficient so that the random component of arrival time inaccuracy due to jitter is much smaller than the steadily increasing arrival t
18、ime inaccuracy caused by system clock frequency error. 3 Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 07/16/2007 01:30:23 MDTNo reproduction or networking permitted without license from IH
19、S -,-,- ISO/IEC 13818-9:1996(E) 0 ISO/IEC 3.2 Testing System Clock Frequency Accuracy, System Clock Slew Rate, and PCR Jitter The compliance test is carried out for one program at a time. The procedure uses a plot of PCR values (which represent the system clock time at which the data was transmitted
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