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Bug 17797 - <video>: Additional AudioTrack.kind categories are needed to identify tracks where audio descriptions are premixed with main dialogue.
Summary: <video>: Additional AudioTrack.kind categories are needed to identify tracks ...
Alias: None
Product: WHATWG
Classification: Unclassified
Component: HTML (show other bugs)
Version: unspecified
Hardware: Other other
: P3 normal
Target Milestone: Unsorted
Assignee: Ian 'Hixie' Hickson
QA Contact: contributor
Depends on:
Reported: 2012-07-18 04:33 UTC by contributor
Modified: 2012-09-16 03:16 UTC (History)
12 users (show)

See Also:


Description contributor 2012-07-18 04:33:35 UTC
This was was cloned from bug 13357 as part of operation convergence.
Originally filed: 2011-07-25 21:14:00 +0000
Original reporter: Bob Lund <>

 #0   Bob Lund                                        2011-07-25 21:14:23 +0000 
Problem statement:

Audio description tracks can come in two forms. In one form, the audio description is a separate track from the video main dialogue. In another form, used by satellite and cable television, audio descriptions are premixed with the main dialogue track. U.S. Cable (and Canada) follow [1] where section 6.4 
Comment 1 Ian 'Hixie' Hickson 2012-07-18 06:47:18 UTC
The text from that bug got weirdly truncated. Here's the most relevant comment though:

=== Bob Lund 2012-02-13 21:55:26 UTC ===
> My intent here is to not add anything until there is at least one format that
> supports this, since there is no point the HTML spec saying to do something
> that can never happen.

Premixed audio descriptions for visually impaired + main dialogue, as required
by the recent FCC ruling
is specified in AC-3 audio used in MPEG-2 TS. This spec
( defines how the presence of
this pre-mixed audio track is signaled: in the  AC-3 bit stream information
syntax (section 5.3.2)  field bsmod = 2 signals the visually impaired audio
stream (see Table 5.7 in section and in the AC-3 descriptor field
full_svc = 1 signals a full audio service (section A4.3), meaning the track
includes the main dialogue audio.

This standard is adhered to in North American broadcast channels. These AC-3
signals could also exist when these channels are redistributed over IP.
Comment 2 contributor 2012-09-16 03:16:24 UTC
Checked in as WHATWG revision r7358.
Check-in comment: Another possible audio track kind