- From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
- Date: Sat, 14 May 2011 13:49:36 +1000
- To: Sean Hayes <Sean.Hayes@microsoft.com>
- Cc: "HTML Accessibility Task Force (public-html-a11y@w3.org)" <public-html-a11y@w3.org>
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] >
Received on Saturday, 14 May 2011 03:50:24 UTC