IEC 61937-4 pdf download Digital audio – Interface for non-linear PCM encoded audio bitstreams applying IEC 60958 Part 4: Non-linear PCM bitstreams according to the MPEG audio format
This part of IEC 61 937 specifies the method for the digital audio interface specified in IEC 60958 to convey non-linear PCM bitstreams encoded in accordance with the MPEG audio.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60958 (all parts), Digital audio interface
IEC 61 937-1 , Digital audio – Interface for non-linear PCM encoded audio bitstreams applying IEC 60958 – Part 1: General
3 Terms and definitions
For the purposes of this document, the following definitions, abbreviations and presentation convention apply.
delay time of an external audio decoder to decode an AC-3 data-burst, defined as the sum of
two values of the receiving delay time and the decoding delay time
Advanced Television Systems Committee
Moving Pictures Expert Group, a joint committee of ISO and IEC
International Telecommunication Union, Radio Communication Bureau
3.3 Presentation convention
Value ‘F872’ in hexadecimal format
4 Mapping of the audio bitstream on to IEC 61 937
The coding of the bitstream and data-burst is in accordance with IEC 61 937-1 .
The 1 6-bit burst-info contains information about the data that will be found in the data-burst (see Table 1 ).
5 Format of MPEG audio data-burst
This clause specifies the audio data-burst of MPEG audio. Specific properties such as reference points, repetition period, method of filling stream gaps and decoding latency are specified.
The decoding latency (or delay), indicated for the data-types, should be used by the transmitter to schedule data-bursts as necessary to establish synchronization between picture and decoded audio.
5.2 Pause data-burst
Pause data-bursts for MPEG audio are given in Table 2.
5.3 Audio data-types
5.3.1 MPEG-1 layer-1 An MPEG-1 layer-1 MPEG-frame represents 384 samples of each encoded channel and can be transferred using data-type 04h. The data-burst is headed with a burst-preamble, followed by the burst-payload.
In the case where pause data-bursts are used to fill stream gaps in the MPEG-1 layer-1 bit- stream as described in IEC 61 937-1 , it is recommended that the pause data-bursts be transmitted with a repetition period of 32 IEC 60958 frames. The total gap length shall be a multiple of 32 IEC 60958 frames.
When a stream gap in an MPEG bitstream is filled by a sequence of pause data-bursts, the Pa of the initial pause data-burst should be located at the 1 6-bit data word located 384 IEC 60958 frames following the Pa of the previous MPEG data-burst. The sequence(s) of pause data-bursts that fill the stream gap shall continue from this point up to the Pa of the first MPEG data-burst which follows the stream gap. The gap-length parameter contained in the pause data-burst may be used to specify the number of decoded PCM samples that are missing (due to the gap).