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AC-3 Descriptor
Association Tag Descriptor
ATSC Private Information Descriptor
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Descriptor logo

AC-3 AudioDescriptor [ATSC Semantics]

The ATSC AC-3 descriptor is a descriptor that should be located in the Program Map Table of an ATSC program service as well as in the Event Information Table of any program event currently being transmitted in a virtual channel.

Pursuant to the ATSC A/53 specification, the AC-3 descriptor is mandatory to describe ATSC elementary streams that carry AC-3 audio.  As the Federal Communications Commission has incorporated A/52 and A/53 by reference into section 73.8000 of it's rules, this is ___ for all U.S. digital broadcast television stations.

The ATSC AC-3 descriptor is listed in Table 6.25a and b of the ATSC A/65 specification, but the descriptor is defined in Annex A of the ATSC A/52 (AC-3) specification.

Note: the below only includes elements appropriate to ATSC A/52 AC-3, and reflects the AC-3_audio_stream_descriptor as defined in ATSC A/52B (2005)

descriptor syntax
syntaxbit index# of bitsmnemonic
descriptor_tag08uimsbf
descriptor_length88bslbf
sample_rate_code163uimsbf
bsid195uimsbf
bit_rate_code246uimsbf
surround_mode302bslbf
bsmod323bslbf
num_channels354bslbf
full_svc391uimsbf
langcod408uimsbf
if num_channels==0
  langcod2488uimsbf
if bsmod<2
  mainid483uimsbf
  priority512uimsbf
  reserved533'111'
else
  asvcflags488uimsbf
end if
textlen56  7'0000000'
text_code63 1'0'
language_flag 64 1bslbf
language_flag_265 1'0'
reserved 666'111111'
if language_flag == 1
  language 723*8uimsbf
end if
legend
Note: bit index is only indicated for the first time through the descriptor.

See: Descriptors Generally

 

This page was modified on October 10, 2010 to reflect the latest version of the AC-3 descriptor and to change the name of the descriptor to the latest version.

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