1、 Copyright 2015 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue., White Plains, NY 10601 (914) 761-1100 Approved November 6, 2015 Table of Contents Page Foreword 2 Intellectual Property . 2 1 Scope 3 2 Conformance Notation 3 3 Normative References 3 4 Definitions and Acrony
2、ms . 4 4.1 Definitions 4 4.2 Acronyms . 5 5 AC-4 5 5.1 Overview 5 5.2 burst_preamble 6 5.3 AC-4 Burst Payload 8 5.4 AES3 Frame Rate (Sampling Frequency) . 8 5.5 AC-4 Reference Point 9 5.6 AC-4 Standard Repetition Rate . 9 5.7 AC-4 Standard Decode Latency 10 5.8 AC-4 Reference Position 10 5.9 AC-4 Gu
3、ard Band . 12 5.10 Burst Payload Timing . 13 5.11 Use of Pause Data Bursts Between AC-4 Data Bursts . 13 Annex A AC-4 Sync Frame 14 Annex B Bibliography (Informative) . 16 Page 1 of 16 pages SMPTE ST 2101:2015 SMPTE STANDARD Format for Non-PCM Audio and Data in AES3 AC-4 Data Type SMPTE ST 2101:2015
4、 Page 2 of 16 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an internationally-recognized standards developing organization. Headquartered and incorporated in the United States of America, SMPTE has members in over 80 countries on six continents. SMPTEs Engineering
5、 Documents, including Standards, Recommended Practices, and Engineering Guidelines, are prepared by SMPTEs Technology Committees. Participation in these Committees is open to all with a bona fide interest in their work. SMPTE cooperates closely with other standards-developing organizations, includin
6、g ISO, IEC and ITU. SMPTE Engineering Documents are drafted in accordance with the rules given in Standards Operating Manual. SMPTE ST 2021 was prepared by Technology Committee 32NF. Intellectual Property At the time of publication no notice had been received by SMPTE claiming patent rights essentia
7、l to the implementation of this Engineering Document. However, attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. SMPTE shall not be held responsible for identifying any or all such patent rights. SMPTE ST 2101:2015 Page 3 of 16 page
8、s 1 Scope This standard describes how AC-4 data rate reduced (non PCM) audio streams conforming to ETSI TS 103 190 are packed into an AES3 data stream, following the methods described by SMPTE ST 337. The AC-4 data type is identified by a data type number listed in SMPTE ST 338 and carried in the bu
9、rst information word of the data burst preamble. 2 Conformance Notation Normative text is text that describes elements of the design that are indispensable or contains the conformance language keywords: “shall“, “should“, or “may“. Informative text is text that is potentially helpful to the user, bu
10、t not indispensable, and can be removed, changed, or added editorially without affecting interoperability. Informative text does not contain any conformance keywords. All text in this document is, by default, normative, except: the Introduction, any section explicitly labeled as “Informative“ or ind
11、ividual paragraphs that start with “Note:” The keywords “shall“ and “shall not“ indicate requirements strictly to be followed in order to conform to the document and from which no deviation is permitted. The keywords, “should“ and “should not“ indicate that, among several possibilities, one is recom
12、mended as particularly suitable, without mentioning or excluding others; or that a certain course of action is preferred but not necessarily required; or that (in the negative form) a certain possibility or course of action is deprecated but not prohibited. The keywords “may“ and “need not“ indicate
13、 courses of action permissible within the limits of the document. The keyword “reserved” indicates a provision that is not defined at this time, shall not be used, and may be defined in the future. The keyword “forbidden” indicates “reserved” and in addition indicates that the provision will never b
14、e defined in the future. A conformant implementation according to this document is one that includes all mandatory provisions (“shall“) and, if implemented, all recommended provisions (“should“) as described. A conformant implementation need not implement optional provisions (“may“) and need not imp
15、lement them as described. Unless otherwise specified, the order of precedence of the types of normative information in this document shall be as follows: Normative prose shall be the authoritative definition; Tables shall be next; followed by formal languages; then figures; and then any other langua
16、ge forms. 3 Normative References Note: All references in this document to other SMPTE documents use the current numbering style (e.g. SMPTE ST 274:2008) although, during a transitional phase, the document as published (printed or PDF) may bear an older designation (such as SMPTE 274M-2008). Document
17、s with the same root number (e.g. 274) and publication year (e.g. 2008) are functionally identical. The following standards contain provisions that, through reference in this text, constitute provisions of this recommended practice. At the time of publication, the editions indicated were valid. All
18、standards are subject to revision, and parties to agreements based on this recommended practice are encouraged to investigate the possibility of applying the most recent edition of the standards indicated below. ETSI TS 103 190 v.1.1.1 (2014-04), Digital Audio Compression (AC-4) Standard SMPTE RP 16
19、8:2009, Definition of Vertical Interval Switching Point for Synchronous Video Switching SMPTE ST 2101:2015 Page 4 of 16 pages SMPTE ST 274:2008, Television 1920 1080 Image Sample Structure, Digital Representation and Digital Timing Reference Sequences for Multiple Picture Rates SMPTE ST 296:2012, 12
20、80 720 Progressive Image 4:2:2 and 4:4:4 Sample Structure Analog and Digital Representation and Analog Interface SMPTE ST 337:2015, Format for Non-PCM Audio and Data in an AES3 Serial Digital Audio Interface SMPTE ST 339:2015, Format for Non-PCM Audio and Data in AES3 Generic Data Types SMPTE ST 203
21、6-1:2014, Ultra High Definition Television Image Parameter Values for Program Production 4 Definitions and Acronyms 4.1 Definitions 4.1.1 AC-4 frame An AC-4 sync frame, as specified in Annex A. 4.1.2 AC-4 I-frame An independently decodable AC-4 frame, as specified in ETSI TS 103 190. 4.1.3 Audio Fra
22、me Rate The number of AC-4 audio frames per second, indicated by the value of the frame_rate_index bitstream parameter as specified in ETSI TS 103 190. 4.1.4 Base sampling frequency The sampling frequency of the AC-4 bitstream, indicated by the value of the fs_index bitstream parameter as specified
23、in ETSI TS 103 190. 4.1.5 Fractional frame rates AC-4 supports a number of fractional audio frame rates. These frame rates are written in shorthand notation, as specified in Table 1. Table 1 Shorthand notation for fractional frame rates Fractional AC-4 audio frame rate (fps) Shorthand version 24 x 1
24、 000 / 1 001 23.976 30 x 1 000 / 1 001 29.97 48 x 1 000 / 1 001 47.952 60 x 1 000 / 1 001 59.94 120 x 1 000 / 1 001 119.88 12 000 / 512 23.438 11 025 / 512 21.533 SMPTE ST 2101:2015 Page 5 of 16 pages 4.1.6 Latency Delay time of an external audio decoder to decode an AC-4 data burst, defined as the
25、sum of two values; the receiving delay time and the decoding delay time. 4.2 Acronyms 4.2.1 ETSI European Telecommunication Standards Institute 4.2.2 fps frames per second 4.2.3 UIMSBF Unsigned integer, most significant bit first 5 AC-4 5.1 Overview AC-4 coded audio shall be transported in an AES3 d
26、ata stream as a series of Data Bursts. Each Data Burst shall start with a Burst Preamble as defined by SMPTE ST 337, containing information about the Burst Payload, which shall follow the Burst Preamble. The Burst Payload shall consist of an AC-4 Frame. The Burst Payload shall be followed by enough
27、zero padding words to make the resulting Data Burst duration exactly match the duration in samples of baseband (PCM) audio that the AC-4 coded audio represents. The resulting Data Bursts shall be placed in the audio sample word/aux data fields of AES3 subframes at regular intervals in either the fra
28、me or subframe mode (see SMPTE ST 337, Section 5). Data Bursts shall be placed in the AES3 transport, using either 16, 20, or 24 bits of the available data space. While the 24-bit mode allows more efficient use of the AES3 capacity, the 16- and 20-bit modes allow use with existing equipment limited
29、to 16- or 20-bit operation. A single AC-4 Frame shall form the Burst Payload, as shown in Figure 1. As specified by ETSI TS 103 190 and Annex A of this document, each AC-4 Frame begins with a sync word and a frame size field that indicates the size of the following raw AC-4 frame. If the value of th
30、e sync word is AC41h, the raw AC-4 frame is followed by an error check (crc_word) word. SMPTE ST 2101:2015 Page 6 of 16 pages Figure 1 Structure of an AC-4 data burst (AC-4 frame rate = 23.976 fps) 5.2 burst_preamble The Pc word (burst_info value) of the burst_preamble carries the data_type identifi
31、er, the data_type_dependent and the data_stream_number information (see SMPTE ST 337, Table 7). 5.2.1 data_type identifier The data_type identifier shall be set to 24 (see SMPTE ST 338). 5.2.2 data_type_dependent The values of the data_type_dependent bits shall be as shown in Table 2, and as describ
32、ed below. Table 2 Values of data_type_dependent field for AC-4 data type data_type_dependent bit number Value Meaning 0 3 See Table 3 and Table 4 Repetition rate of the data-burst in AES3 frames 4 Repetition rate flag (rep_rate_flag) The value of bits 0 to 3 of the data_type_dependent field shall in
33、dicate the repetition rate of the AC-4 data-burst. The interpretation of these bits is dependent on the base sampling frequency of the AC-4 bitstream and the AES3 frame rate, as specified in Table 3 and Table 4. Pa AC - 4 Data Burst 2002 Audio Sample periods ( 41 . 7 ms 48 kHz ) Burst Preamble Burst
34、 payload At least two AES 3 frames of padding required The Reference Point is bit 0 of the Pa sync word CRC Word Sync Word Frame Size Raw AC - 4 Frame AC - 4 Sync Frame representing 2002 Audio Sample periods AC - 4 Sync Frame Pb Pc Pd Pa AC - 4 Data Burst 2002 Audio Sample periods ( 41 . 7 ms 48 kHz
35、 ) Burst payload AC - 4 Sync Frame Pb Pc Pd Padding ( silence ) Padding ( silence ) SMPTE ST 2101:2015 Page 7 of 16 pages Table 3 Values of data_type_dependent field for AC-4 at an AES3 frame rate of 48 kHz data_type_dependent bit numbers Value Meaning 0 3 0 Repetition rate of the data-burst in AES3
36、 frames 2002 1 2000 2 1920 3 1601 / 1602 (see Table 7 4 1600 5 1001 6 1000 7 960 8 800 / 801 (see Table 7) 9 800 10 480 11 400 / 401 (see Table 7) 12 400 13 2048 14 15 Reserved 4 Repetition rate flag (rep_rate_flag) Table 4 Values of data_type_dependent field for AC-4 at an AES3 frame rate of 44.1 k
37、Hz data_type_dependent bit numbers Value Contents 0 3 0 12 Reserved 13 Repetition rate of the data-burst in AES3 frames 2048 14, 15 Reserved 4 Repetition rate flag (rep_rate_flag) rep_rate_flag The repetition rate flag shall be set to 0 if the AC-4 data burst is placed in the AES3 interface such tha
38、t the Reference Point of the data burst (see Section 5.5) occurs at the AC-4 standard repetition rate (see Section 5.6). The flag shall be set to 1 if the reference point does not occur at the AC-4 standard repetition rate. This flag is intended to be set to the same state for all data bursts of a g
39、iven AC-4 data stream to indicate whether data bursts for the stream occur at the standard repetition rate. SMPTE ST 2101:2015 Page 8 of 16 pages 5.2.3 data_stream_number The data_stream_number shall be set to any number from 0h to 6h. 7h is a reserved value. See SMPTE ST 337. 5.3 AC-4 Burst Payload
40、 An AC-4 bitstream consists of a sequence of AC-4 frames. The AC-4 burst-payload shall consist of a single AC-4 frame. The length of the AC-4 data-burst will depend on the encoded bit rate (which determines the AC-4 frame length). The specification for the AC-4 bitstream may be found in ETSI documen
41、t TS 103 190. 5.4 AES3 Frame Rate (Sampling Frequency) The frame rate of the AES3 stream used to transport the AC-4 frames shall be the same as the rate at which the encoded audio was sampled. If multiple AC-4 streams are transported in the same AES3 stream, all the audio represented by these Burst
42、Payloads must be sampled at the same rate. The units of burst-length shall be in bits. The maximum size of an AC-4 burst payload is dependent on the repetition rate of the data-burst, and is specified. The maximum data rates shown in Table 5 take into account the two AES3 frames of padding bits betw
43、een data bursts that are required by SMPTE ST 337, Section 7.3 (burst spacing), but does not take into account the use of the AC-4 guard band (specified in Section 5.9). Table 5 AES3 data bit depth and maximum available data rates for AC-4 data Repetition rate of the AC-4 data-burst in AES3 frames A
44、C-4 base sampling frequency Maximum data rate of AC-4 bitstream (kbit/s) 16-bit 20-bit 24-bit 2002 48 kHz 1532.931 1916.164 2299.397 2000 1532.928 1916.160 2299.392 1920 1532.800 1916 2299.200 1601/1602 1532.164 1915.205 2298.246 1600 1532.160 1915.200 2298.240 1001 1529.862 1912.328 2294.793 1000 1
45、529.856 1912.320 2294.784 960 1529.600 1912 2294.400 800/801 1527.944 1909.930 2291.916 800 1528.320 1910.400 2292.480 480 1523.200 1904 2284.800 400/401 1521.423 1901.778 2282.134 400 1520.640 1900.800 2280.960 2048 1533 1916.250 2299.500 2048 44.1 kHz 1408.444 1760.555 2112.666 SMPTE ST 2101:2015
46、Page 9 of 16 pages 5.5 AC-4 Reference Point The reference point of an AC-4 data-burst shall be bit 0 of the Pa sync word, as shown in Figure 1. 5.6 AC-4 Standard Repetition Rate The Standard Repetition Rate of the AC-4 data-burst shall be defined by the base sampling frequency and frame rate of the
47、AC-4 audio bitstream. As AC-4 supports multiple audio frame rates that match commonly used video frame rates, specifically RP 168, ST 274, ST 296 and ST 2036-1 as appropriate, the transmission device shall ensure that the selected AC-4 data-burst repetition rate is equal to the duration of the AC-4
48、frame, as specified in Table 6. Table 6 AC-4 base sampling frequency, AC-4 audio frame rate and corresponding AC-4 data-burst repetition rate AC-4 base sampling frequency AC-4 audio frame rate (fps) AC-4 data-burst repetition rate in AES3 frames 48 kHz 23.976 2 002 24 2 000 25 1 920 29.97 1 601 / 1
49、602 (see Table 7) 30 1 600 47.952 1 001 48 1 000 50 960 59.94 800 / 801 (see Table 7) 60 800 100 480 119.88 400 / 401 (see Table 7) 120 400 23.438 2 048 44,1 kHz 21.533 2 048 For AC-4 audio frame rates of 29.97, 59.94 and 119.88 fps, the duration of an AC-4 audio frame does not correspond to an integer number of AES3 frames. To ensure that precise time alignment is maintained between the AC-4 data-burst and the AC-4 audio frames at these frame rates, the repetition rate of data-bursts varies so that over a sequenc
