Useful Documentation

These documents are available from the ATSC website (www.atsc.org) or ETSI website (www.etsi.org) as appropriate.

 

Dolby Digital and Dolby Digital Plus bitstream syntax

ETSI TS 102 366 V1.3.1 Digital Audio Compression (AC-3, Enhanced AC-3) Standard – August 2014

 

ETSI TS 102 366 covers the syntax of Dolby Digital and Dolby Digital Plus bitstreams.   Notable sections include:-

Section 4 – which defines the original AC-3 syntax

Annex D - which defines an alternative syntax for AC-3 which includes support for additional metadata parameters and is compatible with all AC-3 decoders

Annex E – which defines the E-AC-3 syntax which is not backwards compatible with AC-3 decoders

 

ATSC A/52B - Digital Audio Compression Standard (AC-3, E-AC-3)

Revision B – 17 December 2012

 

ATSC A/52B is almost identical to ETSI TS 102 366.  However, ETSI TS 102 366 includes some optional additions to ATSC A/52B, so is recommended as the main reference document for E-AC-3 bitstream syntax.

Multiplexing Dolby Digital and Dolby Digital Plus in DVB TSs

ETSI TS 101 154 V2.2.1 Digital Video Broadcasting (DVB); Implementation guidelines for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream – June 2015

 

Annex C – Covers the parameters for multiplexing AC-3 and E-AC-3 bitstreams, including definition of the AC-3_descriptor and the Enhanced_AC-3_descriptor.

 

ETSI EN 300 468 V1.15.1 Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems

Multiplexing Dolby Digital and Dolby Digital Plus in ATSC TSs

 

ATSC A/53 Part 1-6 (System) - Digital Television Standard (A/53) – 3 January 2007

 

ATSC A/53 Part 1-6 document defines some requirements for the descriptors for AC-3 and also defines where E-AC-3 can be used.

 

Useful Parameters

stream_type

The stream_type values are shown in the table below.

 

	AC-3	E-AC-3
ATSC	0x81	0x87
DVB	0x06	0x06

 

stream_id

The stream_id value should be 0xBD for all cases covered in this document.

descriptor_tag

The descriptor_tag values are shown in the table below.

 

	AC-3	E-AC-3
ATSC	0x81	0x81
DVB	0x6A	0x7A

 

The complete descriptor for ATSC is defined in ATSC A52/B and the descriptors for DVB are defined in ETSI TS 101 154.

Buffer size

The required buffer sizes for decoders are shown in the table below

 

	AC-3	E-AC-3
ATSC	2592 bytes	5184 bytes
DVB	5696 bytes	5696 bytes

 

Syncword

The syncword defines the start of AC-3 and E-AC-3 frames.  The value for syncword is 0x0B77.

Bitstream ID (bsid)

The bsid parameter of AC-3 and E-AC-3 can be used for differentiating between AC-3 and E-AC-3 streams.  bsid is a 5 bit value.  bsid occurs in bit positions 25-29 from the end of syncword.  A value of bsid between 0 and 8 inclusive indicates an AC-3 stream.  A value of bsid between 11 and 16 inclusive indicates an E-AC-3 bitstream.  Other values of bsid are currently reserved.

 

For a complete definition of bsid see ETSI TS 102 366 (Sections 4 and E.1).

Data rate/Bit rate

Multiplexors, demultiplexors, encoders and decoders must be able to handle changes of audio bit rates seamlessly.  For example, multiplexors must detect the bit rate of the incoming AC-3 or E-AC-3 stream and configure the multiplex accordingly with due consideration for demux/decoder performance, such as decoder buffer models.

 

For AC-3 streams the bit rate is derived from the frmsizecod and fscod parameters.  For the location and definition of these parameters see ETSI TS 102 366.  Table 4.13 in ETSI TS 102 366 shows the relationship between frmsizecod, fscod and bit rate.

 

For E-AC-3 streams the bit rate is derived from frmsiz, fscod, fscod2 and numblkscod.  For the location and definition of these parameters see ETSI TS 102 366 (Section E.1). The relationship between these parameters and bit rate is shown below.

 

 

Bitrate (bps) = Fs * Frmsiz

                            -----------

                            16 * numblks

 

where Fs is the sample rate indicated by fscod and fscod2, and numblks is the number of blocks indicated by fscod and numblkscod.

Bitstream Structure

 

 

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