Tag Archives: Mozilla

“HTML5 Audio And Video Accessibility, Internationalisation And Usability” talk at Mozilla Summit

For 2 months now, I have been quietly working along on a new Mozilla contract that I received to continue working on HTML5 media accessibility. Thanks Mozilla!

Lots has been happening – the W3C HTML5 accessibility task force published a requirements document, the Media Text Associations proposal made it into the HTML5 draft as a <track> element, and there are discussions about the advantages and disadvantages of the new WebSRT caption format that Ian Hickson created in the WHATWG HTML5 draft.

In attending the Mozilla Summit last week, I had a chance to present the current state of development of HTML5 media accessibility and some of the ongoing work. I focused on the following four current activities on the technical side of things, which are key to satisfying many of the collected media accessibility requirements:

  1. Multitrack Video Support
  2. External Text Tracks Markup in HTML5
  3. External Text Track File Format
  4. Direct Access to Media Fragments

The first three now already have first drafts in the HTML5 specification, though the details still need to be improved and an external text track file format agreed on. The last has had a major push ahead with the Media Fragments WG publishing a Last Call Working Draft. So, on the specification side of things, major progress has been made. On the implementation – even on the example implementation – side of things, we still fall down badly. This is where my focus will lie in the next few months.

Follow this link to read through my slides from the Mozilla 2010 summit.

New proposal for captions and other timed text for HTML5

The first specification for how to include captions, subtitles, lyrics, and similar time-aligned text with HTML5 media elements has received a lot of feedback – probably because there are several demos available.

The feedback has encouraged me to develop a new specification that includes the concerns and makes it easier to associate out-of-band time-aligned text (i.e. subtitles stored in separate files to the video/audio file). A simple example of the new specification using srt files is this:

<video src="video.ogv" controls>
   <itextlist category="CC">
     <itext src="caption_en.srt" lang="en"/>
     <itext src="caption_de.srt" lang="de"/>
     <itext src="caption_fr.srt" lang="fr"/>
     <itext src="caption_jp.srt" lang="jp"/>

By default, the charset of the itext file is UTF-8, and the default format is text/srt (incidentally a mime type the still needs to be registered). Also by default the browser is expected to select for display the track that matches the set default language of the browser. This has been proven to work well in the previous experiments.

Check out the new itext specification, read on to get an introduction to what has changed, and leave me your feedback if you can!

The itextlist element
You will have noticed that in comparison to the previous specification, this specification contains a grouping element called “itextlist”. This is necessary because we have to distinguish between alternative time-aligned text tracks and ones that can be additional, i.e. displayed at the same time. In the first specification this was done by inspecting each itext element’s category and grouping them together, but that resulted in much repetition and unreadable specifications.

Also, it was not clear which itext elements were to be displayed in the same region and which in different ones. Now, their styling can be controlled uniformly.

The final advantage is that association of callbacks for entering and leaving text segments as extracted from the itext elements can now be controlled from the itextlist element in a uniform manner.

This change also makes it simple for a parser to determine the structure of the menu that is created and included in the controls element of the audio or video element.

Incidentally, a patch for Firefox already exists that makes this part of the browser. It does not yet support this new itext specification, but here is a screenshot that Felipe Corr

Tracking Status of Video Accessibility Work

Just a brief note to let everyone know about a new wikipage I created for my Mozilla work about video accessibility, where I want to track the status and outcomes of my work. You can find it at https://wiki.mozilla.org/Accessibility/Video_a11y_Aug09. It lists the following sections: Test File Collection, Specifications, Demo implementations using JavaScript, Related open bugs in Mozilla, and Publications.

$100K towards Xiph developers

Today, Wikimedia and Mozilla announced a grant provided by the Mozilla Corporation towards maturing the support of Ogg in the Firefox Web browser. I’m happy to have helped in making the proposal become concrete and now we have the following three Xiph developers working on it:

  • Viktor Gal – the maintainer of liboggplay
  • Conrad Parker – the key developer of multiple Ogg support libraries, in particular liboggz
  • Tim Terriberry – the key developer of Ogg Theora

Viktor will work towards stabilising the current Ogg Theora support in Firefox, Conrad will work towards Ogg network seeking, language selection and improved library support, and Tim will include the new Thusnelda Theora encoder improvements into Theora mainstream.

Looking forward to awesome Firefox video technology!

UPDATE – Other posts on this topic:

Video Accessibility for Firefox

Ogg has struggled for the last few years to recommend the best format to provide caption and subtitle support for Ogg Theora. The OGM fork had a firm focus on using subtitles in SRT, SSA or VobSub format. However, in Ogg we have always found these too simplistic and wanted a more comprehensive solution. The main aim was to have timed text included into the video stream in a time-aligned fashion. Writ, CMML, and now Kate all do this. And yet, we have still not defined which is the one format that we want everybody to support as the caption/subtitle format.

With Ogg Theora having been chosen by Mozilla as the baseline video codec for Firefox and the HTML5 <video> tag, Mozilla is looking to solve this problem in a community fashion: the solution needs to be acceptable to Xiph, supported by Opera who are also experimenting with Ogg Theora, and ultimately provide a proposal to the W3C and WHATWG that can sensibly be included into HTML5.

As a first step in this direction, Mozilla have contracted me to analyse the situation and propose a way forward.

The contract goes beyond simple captions and subtitles though: it analyses all accessibility requirements for video, which includes audio annotations for the blind, sign language video tracks, and also transcripts, karaoke, and metadata tracks as more generic timed text example tracks. The analysis will thus be about how to enable a framework for creating a timed text track in Ogg and which concrete formats should be supported for each of the required functionalities.

While I can do much of the analysis myself, a decision on how to move forward can only be made with lots of community input. The whole process of this analysis will therefore be an open one with information being collected on the Mozilla Wiki, see https://wiki.mozilla.org/Accessibility/Video_Accessibility .

An open mailing list is also set up at Xiph to create a discussion forum for video accessibility: accessibility@lists.xiph.org. Join there if you’d like to provide input. I am particularly keen for people with disabilities to join because we need to get it right for them!

I am very excited about this project and feel honoured for being supported to help solve accessibility issues for Ogg and Firefox! Let’s get it right!