W3C home > Mailing lists > Public > public-html-bugzilla@w3.org > February 2012

[Bug 13357] <video>: Additional AudioTrack.kind categories are needed to identify tracks where audio descriptions are premixed with main dialogue.

From: <bugzilla@jessica.w3.org>
Date: Mon, 13 Feb 2012 21:55:29 +0000
To: public-html-bugzilla@w3.org
Message-Id: <E1Rx3rt-0002VP-AG@jessica.w3.org>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=13357

--- Comment #13 from Bob Lund <b.lund@cablelabs.com> 2012-02-13 21:55:26 UTC ---
(In reply to comment #12)
> 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
(http://transition.fcc.gov/Daily_Releases/Daily_Business/2011/db0825/FCC-11-126A1.pdf),
is specified in AC-3 audio used in MPEG-2 TS. This spec
(http://www.atsc.org/cms/standards/a_52-2010.pdf) 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 5.4.2.2) 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.

-- 
Configure bugmail: https://www.w3.org/Bugs/Public/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are the QA contact for the bug.
Received on Monday, 13 February 2012 21:55:32 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 13 February 2012 21:55:32 GMT