W3C home > Mailing lists > Public > public-html-a11y@w3.org > March 2010

Re: Requirements for external text alternatives for audio/video

From: Geoff Freed <geoff_freed@wgbh.org>
Date: Mon, 15 Mar 2010 15:55:28 -0400
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-ID: <C7C408F2.B260%geoff_freed@wgbh.org>
On 3/14/10 8:08 PM, "Silvia Pfeiffer" <silviapfeiffer1@gmail.com> wrote:

Hi all,


We have 15 voices for SRT and 14 for DFXP.

However, looking at the detailed replies, I can see that we basically
have two camps: one that says "let's just start simple" and the other
that says "we need something that is extensible, incorporates styling
and markup".

What it tells me is that we never really looked at what our
requirements for synchronised text alternatives, and in particular for
caption formats here.

I'd like us to collect these requirements so we can make a better
recommendation as a group. We should look at these requirements from
several view points, some of which may be:
* a legal POV (what do a11y laws require us to do),
* a WCAG requirements POV,
* a a11y user's usability POV,
* an international user's POV,
an anything you can think of that I forgot.

(begin GF)
One item to note is the US Federal Communications Commission (FCC) DTV Decoder Standards, which was adopted in July of 2001.  This document lays out the features that DTV CC decoders in the US must support.  The full doc itself is at http://fjallfoss.fcc.gov/edocs_public/attachmatch/FCC-00-259A1.pdf; I've attached a plain-text excerpt that summarizes the decoder requirements.  These requirements were created after the FCC received numerous comments from the deaf and hard-of-hearing community over the importance of having both authorial and user access to styling features.  The DTV Decoder Standards ensure that CEA-708 captions containing specific styling features (e.g., foreground/background color, translucency, font face and size, etc.) will appear on digital televisions as the author intended.

In the US, providers of online media originating on broadcast or cable TV are complying with the existing requirements which were based on significant public input, and have initiated a technical working group within SMPTE to assure that they can "author once, use often" in terms of the captions they are paying for. These captions are presently automatically translated to CEA-708 caption files with full stylistic mark-up that caption providers would like to see preserved when they are transformed to other delivery formats, rather than be discarded because the target format doesn't support these features.

In terms of compatibility with newer standards, note that the Advanced Television Systems  Committee (ATSC) Mobile DTV Standard (A/153; http://www.atsc.org/standards/a153.php) includes support for the transmission of CEA-708 captions, which as you know contains a range of styling features.  SMPTE-TT will also contain a wide range of caption-style features.

Another thing to keep in mind is that the deaf/hard-of-hearing community has asked specifically for styling features in captions.  Organizations such as Telecommunications for the Deaf, Self Help for Hard of Hearing People, National Association for the Deaf and the AG Bell Association for the Deaf all wrote to the FCC in support of things like foreground/background color, text size and location.  The fact that you do not see these features in wide use today is not a reason to preclude them from future use.  It would be wise to consult with expert users in the deaf and hard-of-hearing community before discarding the capacity for a degree of stylistic mark-up. In fact, the SMPTE working group has established a liaison relationship with the Coalition of Organizations for Accessible Technology, a group of interested parties (numbering more than 300 US national and regional organizations serving deaf or blind people).  The members of this group would certainly have an interest in this discussion.

All this background information is simply to say... promoting a text-display format that does not support minimal styling is, in my view, ignoring the stated needs and desires of the people who rely on captioned media.

Finally, a word about foreign-language subtitles.  Subtitles are frequently displayed over a transparent background.  As such, they usually need coloring, edging or drop-shadow in order to be made clearly visible.  Offering a text-display spec that doesn't support these features won't really help someone trying to make simple subtitles readable over a busy background.

(end GF)


Received on Monday, 15 March 2010 19:56:05 UTC

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