1、 Copyright 2010 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue, White Plains, NY 10601 (914) 761-1100 Approved August 2, 2010 Table of Contents Page Foreword . 2 Intellectual Property 2 Introduction 3 1 Scope . 4 2 Conformance Notation . 4 3 Normative References . 4 4 Defi
2、nitions and Acronyms 5 4.1 Definitions 5 4.2 Acronyms . 6 5 MPEG-4 AAC Data in an ADTS Wrapper 6 5.1 Overview 6 5.2 Burst_preamble 7 5.3 AAC Burst Payload 8 5.4 AES3 Frame Rate (Sampling Frequency) . 8 5.5 AAC Reference Point . 8 5.6 AAC Standard Repetition Rate 8 5.7 AAC Decoding Latency (Professio
3、nal) . 9 5.8 AAC Reference Position 9 5.9 Use of Pause Data Bursts to Fill Gaps in AAC Data Streams . 9 6 MPEG-4 HE AAC Data in an ADTS Wrapper 9 6.1 Overview 9 6.2 Burst_preamble 10 6.3 HE AAC Burst Payload 11 6.4 AES3 Frame Rate (Sampling Frequency) . 11 6.5 HE AAC Reference Point . 11 6.6 HE AAC
4、Standard Repetition Rate 11 6.7 HE AAC Decoding Latency (Professional). 11 6.8 HE AAC Reference Position 12 6.9 Use of Pause Data Bursts to Fill Gaps in HE AAC Data Streams . 12 Page 1 of 18 pages SMPTE ST 2041-3:2010 SMPTE STANDARD Format for Non-PCM Audio and Data in AES3 MPEG-4 AAC and HE AAC Com
5、pressed Digital Audio in ADTS and LATM / LOAS Wrappers SMPTE ST 2041-3:2010 Page 2 of 18 pages 7 MPEG-4 AAC Data in an LATM/LOAS Wrapper 12 7.1 Overview . 12 7.2 Burst_preamble 13 7.3 AAC Burst Payload . 14 7.4 AES3 Frame Rate (Sampling Frequency) 14 7.5 AAC Reference Point . 14 7.6 AAC Standard Rep
6、etition Rate . 14 7.7 AAC Decoding Latency (Professional) . 14 7.8 AAC Reference Position . 14 7.9 Use of Pause Data Bursts to Fill Gaps in AAC Data Streams . 14 8 MPEG-4 HE AAC Data in an LATM/LOAS Wrapper 15 8.1 Overview . 15 8.2 Burst_preamble 16 8.3 HE AAC Burst Payload . 17 8.4 AES3 Frame Rate
7、(Sampling Frequency) 17 8.5 HE AAC Reference Point . 17 8.6 HE AAC Standard Repetition Rate . 17 8.7 HE AAC Decoding Latency (Professional) . 17 8.8 HE AAC Reference Position . 17 8.9 Use of Pause Data Bursts to Fill Gaps in HE AAC Data Streams . 17 Annex A Bibliography (Informative) . 18 Foreword S
8、MPTE (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 Documents, including Standard
9、s, 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, including ISO, IEC and ITU. SMPTE Engi
10、neering Documents are drafted in accordance with the rules given in Part XIII of its Administrative Practices. SMPTE ST 2041-3 was prepared by Technology Committee 32NF. Intellectual Property At the time of publication no notice had been received by SMPTE claiming patent rights essential to the impl
11、ementation of this Standard. 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 2041-3:2010 Page 3 of 18 pages Introduction This sec
12、tion is entirely informative and does not form an integral part of this Engineering Document. The MPEG Committee of ISO/IEC has produced a number of different audio compression technologies. Each of these is nominally an “emission” codec, which means that its design does not include consideration fo
13、r maintaining audio quality in multiple decode re-encode cycles. As a result, many operators will desire to keep the original compressed bitstream intact while routing, switching, and when other baseband manipulations are done with associated video signals. The first of these codecs, MPEG-1 Layer I
14、and II audio (documented in ISO/IEC 11172-3) and MPEG-2 Layers I, II, and III audio (documented in ISO/IEC 13818-3) were intended to be bit-wise compatible within Layers I and II, while MPEG-2 Layer III used “Non-Backwards Compatible” extensions. MPEG-2 Layer III audio has not been widely used in br
15、oadcast, however some recent extensions to it have been added via ISO/IEC 14496-3 Subpart 9 which may result in wider use. The second of these codecs, MPEG-2 AAC (documented in ISO/IEC 13818-7) is intentionally non-compatible with Layer I, II, or III, and is known as “Advanced Audio Coding.” A secon
16、d set of documents, which extended MPEG-2 AAC were documented as a part of MPEG-4 in ISO/IEC 14496-3. Although MPEG-4 AAC was intended to be backwards compatible with MPEG-2 AAC, no assumption should be made that an MPEG-2 decoder can decode an MPEG-4 AAC bitstream (largely due to the different tran
17、sport wrappers). When the SBR tool was added to AAC, creating “HE AAC,” it was documented in Amendments to both ISO/IEC 13818-7 and ISO/IEC 14496-3. It should be noted that there are two alternative “wrappers” standardized for AAC/HE AAC, one called ADTS (widely used in Japanese Digital Broadcasting
18、) and the other known as LATM/LOAS, since the MPEG-4 (ISO/IEC 14496-3) AAC codecs introduced new features and capabilities that require a transport format which can signal their contents. In order to be able to pass the audio bitstream without the necessity to do partial decoding to locate flags the
19、 wrapper was devised. LATM/LOAS is specified as the wrapper for MPEG-4 AAC/HE AAC audio streams within DVB transport stream broadcasting applications. As a result, this suite of SMPTE standards will document carriage of both. The following suite of SMPTE standards defines the carriage of MPEG compre
20、ssed audio bitstreams within an AES3 carrier bitstream: SMPTE ST 2041-1, Format for Non-PCM Audio in AES3 MPEG-1/MPEG-2 Layers I, II, and III Audio SMPTE ST 2041-2, Format for Non-PCM Audio in AES3 MPEG-2 AAC/HE AAC Audio in ADTS SMPTE ST 2041-3, Format for Non-PCM Audio and Data in AES3 MPEG-4 AAC
21、and HE AAC Compressed Digital Audio in ADTS and LATM/LOAS Wrappers The bitstreams defined in this standard can be carried independently of video as AES3 bitstreams or embedded into SDI or HD-SDI bitstreams in the normal manner specified by other SMPTE standards. SMPTE ST 2041-3:2010 Page 4 of 18 pag
22、es 1 Scope This Standard specifies the method of packing MPEG-4 AAC and MPEG-4 HE AAC data rate reduced audio streams contained in either an ADTS or an LATM/LOAS wrapper into an AES3 transport stream. It also specifies the content of the data_type_dependent field of the burst_info (Pc) word of the S
23、ynchronization preamble used to signal the wrapper type and other necessary information about the payload. The Standard specifies the repetition rate, reference point, decoding latency and use of Pause data bursts in interrupted streams. This Standard supports the MPEG-4 AAC Profile, the MPEG-4 High
24、 Efficiency AAC Profile, and the MPEG-4 High Efficiency AAC v2 Profile. This Standard is limited to carriage of a single audio elementary stream. 2 Conformance Notation Normative text is text that describes elements of the design that are indispensable or contains the conformance language keywords:
25、“shall“, “should“, or “may“. Informative text is text that is potentially helpful to the user, but 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 def
26、ault, normative, except: the Introduction, any section explicitly labeled as “Informative“ or individual 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.
27、 The keywords, “should“ and “should not“ indicate that, among several possibilities, one is recommended 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
28、 or course of action is deprecated but not prohibited. The keywords “may“ and “need not“ indicate 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 k
29、eyword “forbidden” indicates “reserved” and in addition indicates that the provision will never be defined in the future. 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 definit
30、ion; Tables shall be next; followed by formal languages; then figures; and then any other language forms. 3 Normative References The following standards contain provisions which, through reference in this text, constitute provisions of this recommended practice. At the time of publication, the editi
31、ons indicated were valid. All 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. AES3-2009, AES Standard for Digital Audio Engineering Seri
32、al Transmission Format for Two-Channel Linearly Represented Digital Audio Data ISO/IEC 13818-7:2006, Information Technology Generic Coding of Moving Pictures and Associated Audio Information Part 7: Advanced Audio Coding (AAC) SMPTE ST 2041-3:2010 Page 5 of 18 pages ISO/IEC 14496-3, Information Tech
33、nology Coding of Audio-Visual Objects Part 3: Audio SMPTE 337-2008, Format for Non-PCM Audio and Data in an AES3 Serial Digital Audio Interface SMPTE ST 338:2010, Format for Non-PCM Audio and Data in AES3 Data Types SMPTE 339-2008, Television Format for Non-PCM Audio and Data in AES3 Generic Data Ty
34、pes SMPTE RP 168-2009, Definition of Vertical Interval Switching Point for Synchronous Video Switching 4 Definitions and Acronyms 4.1 Definitions 4.1.1 AAC LC AAC Profile The MPEG-4 AAC Profile is the counterpart to the MPEG-2 AAC Low Complexity Profile, In contrary to the MPEG-2 AAC LC Profile the
35、MPEG-4 AAC Profile enables the usage of an additional tool. This profile is used when there are restrictions on the usage of RAM and processing complexity. 4.1.2 Access Unit Smallest entity to which timing information can be attributed. An access unit is the smallest individually decodable unit. A d
36、ecoder consumes access units. 4.1.3 adts_error_check( ) An MPEG-4 ADTS element that carries a CRC value which provides protection for the headers and some of the payload. 4.1.4 AudioMuxElement(1) An MPEG-4 LATM element that carries payload data for at least one audio elementary stream, related paylo
37、ad length information and multiplex configuration information. This element carries payload data in form of PayloadMux elements. The number in brackets indicates multiplexing configuration (StreamMuxConfig() is multiplexed into AudioMuxElement(), i.e. in-band transmission. 4.1.5 HE AAC High Efficien
38、cy AAC Profile This Profile utilizes the Spectral Band Replication (SBR) tool in conjunction with AAC. This Profile is a superset of the AAC Profile. For further information please refer to ISO/IEC 14496-3. 4.1.6 HE AAC v2 High Efficiency AAC v2 Profile This Profile utilizes the Spectral Band Replic
39、ation (SBR) tool and the Parametric Stereo (PS) tool in conjunction with AAC. This Profile is a superset of the High Efficiency AAC Profile. For further information please refer to ISO/IEC 14496-3. 4.1.7 MPEG Surround A technology used for coding of multichannel signals based on a downmixed signal o
40、f the original multichannel signal, and associated spatial parameters. Defined by ISO/IEC 23003-1 SMPTE ST 2041-3:2010 Page 6 of 18 pages 4.1.8 PayloadMux Payload data chunk in an AudioMuxElement that contains potentially multiplexed payload data for multiple audio elementary streams. In general Pay
41、loadMux elements can be concatenated inside AudioMuxElements. 4.1.9 StreamMuxConfig Configuration structure that describes the structure of the LATM payload multiplex. 4.1.10 Sub-data-type Reference to the type of payload of the data-bursts defined for the use with the specified data-type 4.1.11 Vid
42、eo Sync Point Signal Alignment Point as defined by Annex A of RP 168. 4.2 Acronyms ADTS: Audio Data Transport Stream, a wrapper structure defined in ISO/IEC 13818-7 and ISO/IEC 14496-3, consisting of a fixed header, a variable header, an optional error check (CRC_check) and a specified number of raw
43、_data_blocks( ). The fixed header of the ADTS contains the syncword plus all parts of the header which are necessary for decoding and which do not change from frame to frame. The variable header of the ADTS contains header data which changes from frame to frame. The ADTS only supports a raw_data_str
44、eam( ) with only one program. The program can have up to 7 channels plus an independently switched coupling channel. LATM: Low overhead Audio Transport Multiplex. A multiplexing layer defined by ISO/IEC 14496-3, used for multiplexing of audio elementary streams. This Standard is limited to transport
45、 of a single audio elementary stream. LOAS: Low Overhead Audio Stream. A synchronization layer defined by ISO/IEC 14496-3. Provides 3 types of formats which are specifically suited for being used on different type of underlying transmission layers depending on their characteristics. MDCT: Modified D
46、iscrete Cosine Transformation SBR: Spectral Band Replication 5 MPEG-4 AAC Data in an ADTS Wrapper When MPEG-4 AAC coded audio is wrapped in ADTS transport syntax it shall be placed into AES3 data streams as specified below. 5.1 Overview MPEG-4 AAC coded audio shall be transported in an AES3 data str
47、eam as a series of Data Bursts. Each Data Burst shall start with a Burst Preamble as defined by SMPTE 337, containing information about the Burst Payload, which shall follow the Burst Preamble. The Burst Payload shall consist of an AAC ADTS Frame. The Burst Payload shall be followed by enough paddin
48、g words (which shall be PCM zeros, or digital silence) to make the resulting Data Burst duration exactly match that of either 960 or 1024 samples of baseband (PCM) audio that the coded audio represents. SMPTE ST 2041-3:2010 Page 7 of 18 pages The resulting Data Bursts shall be placed in the audio sa
49、mple word/aux data fields of AES3 subframes at regular intervals in either the frame or subframe mode (see SMPTE 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 to 16- or 20-bit operation. A single AAC ADTS Frame shall form the Burst Payload, as shown by Figure 1. As specified by ISO/IEC 14496-3, each ADTS
