17797 2012-07-18 04:33:35 +0000 <video>: Additional AudioTrack.kind categories are needed to identify tracks where audio descriptions are premixed with main dialogue. 2012-09-16 03:16:24 +0000 1 1 1 Unclassified WHATWG HTML unspecified Other other RESOLVED FIXED P3 normal Unsorted 1 contributor ian annevk b.lund c.stevens eric.carlson glenn ian jfoliot laura.lee.carlson mark_vickers mike philipj silviapfeiffer1 contributor oldest_to_newest 70061 0 contributor 2012-07-18 04:33:35 +0000 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 <b.lund@cablelabs.com> ================================================================================ #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 70083 1 ian 2012-07-18 06:47:18 +0000 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 (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. 73973 2 contributor 2012-09-16 03:16:24 +0000 Checked in as WHATWG revision r7358. Check-in comment: Another possible audio track kind http://html5.org/tools/web-apps-tracker?from=7357&to=7358