Despite the emergence of the <video> element in HTML 5, Shockwave Flash is still the defacto standard for publish multimedia on the Web. Macromedia, and now Adobe have improved the support for assistive technologies and software interfaces like Microsoft Active Accessibility (MSAA) within the Flash browser plug-ins and it is now possible to create a video player in which all the controls and status information are perceivable by screen reader users. So all the challenges to do with Flash have been overcome, no problems? Wrong.

I and others have uncovered what appears to be a little publicised or little known flaw that renders some of the "embed codes" displayed at sites like YouTube, Vimeo et al completely inaccessible.

Screen shot, wmode = window - default, OK

Recently I've been evaluating Flash media players and I noticed that while many players were fairly accessible, one was not at all. Initially I blamed the media player itself, but then I noticed that the wmode parameter in it's embed code was set to opaque. Further tests have revealed that anything but the default value window completely hides the Flash player from MSAA and therefore screen readers. Web Accessibility in Mind note this as a technique to hide decorative Flash. Stephanie Sullivan has also written about this (2nd to last paragraph), however I think the advice in these articles leaves something to be desired. The Flash content of a page, for example when you embed a movie in a blog post, is often not eye candy, it's the whole focus of the page. And providing 'text-only' alternatives in the blanket fashion suggested at 'lessfussdesign' is often a bad idea.


<object data="player.swf">
    <param name="wmode" value="window" />


    <param name="wmode" value="opaque" />
    <param name="wmode" value="transparent" />

My tips are to avoid setting the wmode parameter unless you absolutely have to (that is, stick with the default value), and if you must, then provide a full HTML/Javascript user-interface (that is, all buttons and status/progress information). An example is Christian Heilmann's excellent Easy YouTube ('wmode' is not set to opaque/transparent in this case, I hasten to add).

Screen shot, wmode = opaque - inaccessible

I tested with Inspect32, part of the Microsoft Active Accessibility kit and the NVDA screen reader.

I'm currently working on fixes for the oohEmbed code (also here) and the Drupal video filter module. The premise for these fixes is that in at least 90% of the cases where this code is used the default for wmode is acceptable.

Feel free to comment on any other embed code or software which needs fixing – and volunteer to submit fixes! (23 September 2009.)

Background: Web Accessibility in Mind (WebAIM) - Flash techniques.


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trabajamos con ellos día a día en función de sus necesidades para eliminar cualquier tipo de barrera que impida su formación académica», aseguró.

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Regarding oohEmbed


Just found your post while looking through the referral logs of! I am no accessibility expert so I am definitely looking forward to your patches to oohembed regarding this wmode issue.

Would the patch just amount to stripping the wmode parameter out of the embed code? If so, I can apply the patch myself one of these days.

Would it be okay with you if

Would it be okay with you if I linked to this page from my website? Just asking since some people don't allow linking to their sites if you don't take their permission.

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1 line patch for Moodle etc.

Hi antricx,

First, thanks for popping by, and apologies for not responding sooner.

Yes to your question, the patch just involves removing the "wmode" parameter - I haven't yet created patches for oohembed etc.

However, I've just created one for Moodle (a project I'm more familiar with). And I've been spreading the word where possible ;)