- From: Janina Sajka <janina@rednote.net>
- Date: Sat, 14 May 2011 21:25:20 -0400
- To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
- Cc: Sean Hayes <Sean.Hayes@microsoft.com>, "HTML Accessibility Task Force (public-html-a11y@w3.org)" <public-html-a11y@w3.org>
Amazing how much easier it is to find information when you can search on the name everyone else has been using! Thanks, Sean, for ferreting out this critical datum. Yes, I believe we should adjust our docs and requests. No reason to go against the flow. With respect to independently adjusting volume of channels (or their pan positions, etc), may I suggest we've asked for that in our User Requirements? * (DV-5) Allow the author to independently adjust the volumes of * the audio description and original soundtracks. * (DV-6) Allow the user to independently adjust the volumes of * the audio description and original soundtracks, with the user's settings overriding the author's. * (DV-8) Allow the author to provide * fade and pan controls to be * accurately synchronised with the * original soundtrack. * (DV-11) Support the simultaneous playback of both the described * and non-described audio tracks so that one may be directed at separate outputs (e.g., a speaker and headphones). Janina Silvia Pfeiffer writes: > On Sat, May 14, 2011 at 1:33 PM, Silvia Pfeiffer > <silviapfeiffer1@gmail.com> wrote: > > Ha, that's funny: have we been using the wrong term all the time? > > > > In out requirements it's called "clear audio" (and that's also what we > > have requested in the bug, see > > http://www.w3.org/Bugs/Public/show_bug.cgi?id=12544 ). In these > > documents it's called "clean audio". > > > > I think we will need to change our documents/request for @kind label... > > > > I've now (using the proper name) also found this document: > > http://www.etsi.org/deliver/etsi_ts/101100_101199/101154/01.09.01_60/ts_101154v010901p.pdf > > which is "Digital Video Broadcasting (DVB); Specification for the use > > of Video and Audio Coding in Broadcasting Applications based on the > > MPEG-2 Transport Stream" . Annex E talks about Clean Audio as a > > supplementary audio service in the form of receiver-mixed data. This > > is in contrast to broadcast-mixed delivery, which would be as a > > separate alternative audio stream, which DVB does not support. > > > > So, it seems that while we are asking for a @kind="clean audio" label > > on audio tracks that are delivered separately to the main audio track > > and provide a better understandable audio mix, this isn't actually > > what DVB supports (and I assume DVB is the only way in which clean > > audio is currently realized?). > > > > So, the question is: what do we do in HTML5 to support the kind of > > clean audio tracks that DVB expects. > > > > IIUC, the receiver-mixed means of delivery of clean audio (and audio > > description for that matter) delivers it through multi-channel audio > > but within the main audio track. This means, on a 3, 5.1 or more audio > > channel file, some of these channels are reserved for non-main audio. > > Actually, that's incorrect for audio description. A "supplementary > audio" channel is an additional audio channel, so it would take up the > number of audio file with stereo, they would deliver 3 channels, for > one with 5.1 it would have 7 channels etc. I think though for clean > audio it is still true that they use center channel for speech only in > a 5.1 file. > > Now the big question is: how common is all this. And would we > encourage people to rather provide multitrack than multichannel for > accessibility needs? > > Cheers, > Silvia. > > > > There is a marker of "visual impaired commentary" for AD and "hearing > > impaired" for clean audio used on the individual channels that have a > > separate use. > > > > The images shown in the spec show the use of clean audio only in the > > case of 5.1 channels with the center channel used for clean audio, > > while when using audio description it shows the use of 3 channels: > > left, right, and a mono audio description.The user has the possibility > > to separately increase the volume of the audio description and of the > > clean audio. > > > > If such a file with multiple audio channels was to be used in a HTML5 > > page, we wouldn't get the same level of control that DVB has defined, > > because there is no control that allows to change the volume mix of > > multi-channel audio. It is important to understand that there is a > > difference between multi-channel audio and multi-track audio: > > multi-channel audio is encoded within one audio track just by > > interleaving the channels within that track. In HTML5 we don't have a > > means to change the volume of the individual channels, but only to > > change the volume of a track. > > > > Cheers, > > Silvia. > > > > > > On Fri, May 13, 2011 at 7:59 PM, Sean Hayes <Sean.Hayes@microsoft.com> wrote: > >> Here is a summary of the European digital television definition for clean > >> audio [adapted from a forthcoming edition of TS 101 154 from the DVB]. The > >> system relies on client side mixing, under control of the programme-maker. > >> > >> > >> > >> Clean Audio refers to audio providing improved intelligibility. It is > >> targeted for viewers with hearing impairments, but can as well serve as > >> improvement for listening in noisy environments.… an important requirement > >> is to adjust, on a passage by passage basis, the relative level of programme > >> sound in the mix which the secondary audio user hears. The programme maker > >> is best able to determine the level under controlled conditions when > >> authoring the secondary audio information to modulate the level of programme > >> sound in the secondary audio capable receiver so suitable secondary audio > >> information is thus transmitted within the secondary audio stream. > >> > >> > >> > >> Individual secondary audio users will have different aural acuity, and there > >> are, in practice, differences in audio signal level for different home > >> receivers. An essential requirement is for the user to be able to adjust the > >> volume to suit his/her condition. > >> > >> > >> > >> A descriptor is sent in a service to indicate a clean audio service. The > >> level by which the main audio service should be attenuated is sent in the > >> metadata (on a per channel basis). The client should accentuate the levels > >> of the channel containing the dialogue and attenuate the other channels, > >> accordingly. The level of the centre channel added should additionally be > >> under user control to allow individual tailoring of the sound for > >> audibility. > >> > >> > >> > >> Background: > >> http://www.rnid.org.uk/VirtualContent/84923/background_noise_PDF.pdf > >> > >> European HD TV requirements: http://tech.ebu.ch/docs/tech/tech3333.pdf [p15] > > -- Janina Sajka, Phone: +1.443.300.2200 sip:janina@asterisk.rednote.net Chair, Open Accessibility janina@a11y.org Linux Foundation http://a11y.org Chair, Protocols & Formats Web Accessibility Initiative http://www.w3.org/wai/pf World Wide Web Consortium (W3C)
Received on Sunday, 15 May 2011 01:25:55 UTC