Semantics for the Enhanced AC-3 descriptor

These are the semantics of the parameters within the E-AC-3 descriptor for a Dolby Digital Plus bitstream.

• The descriptor_tag must be set to is 0xCC.
• The descriptor_length field specifies the total number of bytes of the data portion of the descriptor following the byte defining the value of this field. The minimum length of the descriptor is three bytes, but it may be longer depending on the use of the subsequent descriptor flags.
• The bsid_flag must be set to 1 when the optional bsid field is present in the descriptor.
• The mainid_flag, asvc_flag, and mixinfoexists parameters must be set to 0.
• The substream1_flag must be set to 1 when the Dolby Digital Plus stream contains an additional associated audio service in independent substream 1. If an independent substream with a substreamid value of 1 is not present in the bitstream, the substream1_flag must be set to 0.
• The substream2_flag parameter must be set to 1 when the Dolby Digital Plus stream contains an additional associated audio service in independent substream 2. If an independent substream with a substreamid value of 2 is not present in the bitstream, the substream2_flag flag must be set to 0.
• The substream3_flag parameter must be set to 1 when the Dolby Digital Plus stream contains an additional associated audio service in independent substream 3. If an independent substream with a substreamid value of 3 is not present in the bitstream, this flag must be set to 0.
• The value of the one-bit full_service_flag indicates whether the audio service in independent substream 0 (and any dependent substreams associated with independent substream 0) of the Dolby Digital Plus stream is full-service audio, suitable for presentation, or whether this audio service is only a partial service that should be combined with another audio service before presentation. The value must be set according to these criteria:
  • If the audio service is sufficiently complete for presentation without being combined with another audio service (for example, a visually impaired service containing all elements of the program, including music, effects, dialogue, and a narrative description of the visual program content), the full_service_flag must be set to a value of 1.
  • If the service is not sufficiently complete must be combined with another audio service (for example, a visually impaired service containing only a narrative description of the visual program content, which must be combined with another audio service containing music, effects, and dialogue), the full_service_flag must be set to a value of 0.
• The service_type field indicates the type of audio service being conveyed in independent substream 0 (and any dependent substreams associated with independent substream 0) of the Dolby Digital Plus stream. The service_type field must be interpreted as listed in the table.

  Table 1. Service type field

  Field value	Description	Restrictions1
  		Full-service flag	Number of channels field
  000	Complete Main (CM)	Must be set to 1
  001	Music and Effects (ME)	Must be set to 0
  010	Visually Impaired (VI)
  011	Hearing Impaired (HI)
  100	Dialogue (D)	Must be set to 0
  101	Commentary (C)
  110	Emergency (E)	Must be set to 1	Must be set to 000
  111	Voiceover (VO)	Must be set to 0	Must be set to 000
  111	Karaoke	Must be set to 1	Must be set to 010, 011, or 100

• The number_of_channels field (three bits) indicates the number of channels present in independent substream 0 (and any dependent substreams associated with independent substream 0) of the Dolby Digital Plus stream. This field must be interpreted as listed in the number of channels field table:
  • The language_flag (one bit) indicates whether the language field (three bytes) is present in the descriptor. If the language field is present, then this bit must be set to 1. If the language field is not present, then this bit must be set to 0.
  • The language_flag_2 must be set to 0.
  • The bsid field (five bits) indicates the Dolby Digital Plus coding version. If the bsid field is included, the value of the field must be set to the same value as the bsid parameter in independent substream 0 of the Dolby Digital Plus stream.

  Table 2. Number of channels field

  Field value2	Description	Restrictions3
  		Full-service flag	Service type field
  000	Mono
  001	1+1 mode
  010	Two channel
  011	Two channel encoded in Dolby Surround
  100	Multichannel audio (greater than two channels and up to 5.1 channels)
  101	Multichannel audio (greater than 5.1 channels)	Must be set to 1	Must be set to 000
  110	Reserved for future use
  111	Reserved for future use

• The substream1 field (eight bits) indicates the type of audio carried in independent substream 1 of the Dolby Digital Plus stream. The value assignments of each bit are indicated in the substream field bit value assignments table. If the Dolby Digital Plus bitstream contains an independent substream with a substreamid value of 1, the PMT must include the substream1 field.
• The substream2 field (eight bits) indicates the type of audio carried in independent substream 2 of the Dolby Digital Plus stream. The value assignments of each bit are indicated in the substream field bit value assignments table. If the Dolby Digital Plus bitstream contains an independent substream with a substreamid value of 2, the PMT must include the substream2 field.
• The substream3 field (eight bits) indicates the type of audio carried in independent substream 3 of the Dolby Digital Plus stream. The value assignments of each bit are indicated in the substream field bit value assignments table. If the Dolby Digital Plus bitstream contains an independent substream with a substreamid value of 3, the PMT must include the substream3 field.

  Table 3. Substream field bit value assignments

  Substream 1–3 bits	Description
  b7 (most-significant bit)	Reserved (must be set to 1)
  b6	Reserved (must be set to 0)
  b5 to b3	Service type flags (see the Service type flags table)
  b2 to b0	Number of channels flags (see the Number of channels flags table)

  Table 4. Service type flags

  Bit values			Description	Restrictions4
  b5	b4	b3		Number of channels field
  0	0	0	Reserved
  0	0	1	Music and Effects (ME)
  0	1	0	Visually Impaired (VI)
  0	1	1	Hearing Impaired (HI)
  1	0	0	Dialogue (D)
  1	0	1	Commentary (C)
  1	1	0	Reserved
  1	1	1	Voiceover (VO)	Must be set to 000

  Table 5. Number of channels flags

  Flags			Description
  b2	b1	b0
  0	0	0	Mono
  0	0	1	Reserved for future use
  0	1	0	Two channel5
  0	1	1	Two channel encoded in Dolby Surround
  1	0	0	Multichannel audio (greater than two channels and up to 5.1 channels)
  1	0	1	Reserved for future use
  1	1	0	Reserved for future use
  1	1	1	Reserved for future use

• The substream1, substream2, and substream3 field must be set to values that are indicated in the tables in this section. The respective substream field may be ignored if other values are conveyed:
  • The language field (three bytes) defines the language of this audio service. The language field must contain a three-character code as specified by ISO 639-2. Each character is coded into eight bits according to ISO 8859-1 (ISO Latin-1) and inserted in order into the 24-bit field. The coding is identical to that used in the MPEG-2 ISO_639_language_code value in the ISO_639_language_descriptor specified in ISO/IEC 13818-1.
  • The additional_info field provides optional bytes for future use.