Techniques for WCAG 2.0

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FLASH34: Turning off sounds that play automatically when an assistive technology is detected


This technique relates to:

User Agent and Assistive Technology Support Notes

See User Agent Support for Flash for general information on user agent support.


The intent of this technique is to prevent sounds from playing when the Flash movie loads. This is useful for those who utilize assistive technologies (such as screen readers, screen magnifiers, switch mechanisms, etc.) and those who may not (such as those with cognitive, learning and language disabilities). By default, the sound will be played automatically. When a screen reader such as JAWS is detected however, the sound will have to be started manually.

To perform screen reader detection, Flash provides the property. If this property is set to true, it means that the Flash player has detected running assistive technology. Based on this flag, the Flash developer can choose to run different functionality.

Note 1: The Flash player requires some time to detect active assistive technology and set the property. To get accurate results, do not check for this property immediately on the first frame of the movie. Instead, perform the check 5 frames in or based on a timed event.

Note 2: Not every screen reader will be detected using this mechanism. In general, the property will be set to true when any MSAA client is running.

Note 3: Other assistive technology tools, including screen magnifiers, or tools not used as assistive technologies may also utilize MSAA in ways that result in being set to true.


Example 1: A SoundHandler class

A class called SoundHandler is created which automatically starts playing an mp3 file only when is set to false. Note that this example also checks the flash.system.Capabilities.hasAccessibility property. This property does not check whether a screen reader is running, but instead indicates whether the Flash player is running in an environment that supports MSAA (which basically means the Windows operating system).

Example Code:

package wcagSamples {
  import flash.accessibility.Accessibility;
  import flash.display.Sprite;
  import flash.system.Capabilities;
  import fl.controls.Button;
  import fl.accessibility.ButtonAccImpl;
  import fl.controls.Label;
  public class SoundHandler extends Sprite {
    private var snd: Sound = new Sound();
    private var button: Button = new Button();
    private var req: URLRequest = new URLRequest(
    private var channel: SoundChannel = new SoundChannel();
    private var statusLbl: Label = new Label();
    public function SoundHandler() {
      button.x = 10;
      button.y = 10;
      statusLbl.autoSize = "left";
      statusLbl.x = 10;
      statusLbl.y = 40;
      button.addEventListener(MouseEvent.CLICK, clickHandler);
      if (! Capabilities.hasAccessibility || ! {
        channel =;
        button.label = "Stop Sound";
        statusLbl.text = "No Assistive technology detected. \
          Sound will play automatically";
      } else {
        button.label = "Start Sound";
        statusLbl.text = "Assistive technology detected. \
          Sound will not play automatically";
    private function clickHandler(e: MouseEvent): void {
      if (button.label == "Stop Sound") {
        button.label = "Start Sound";
      } else {
        channel =;
        button.label = "Stop Sound";

This technique can be viewed in the working version of A SoundHandler class. The source of A SoundHandler class is available.


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  1. Start a screen reader that supports MSAA.

  2. Open a page containing a Flash movie that starts playing audio automatically when a screen reader is not running

  3. Confirm that the audio is stopped.

Expected Results

  1. #3 is true

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.

Techniques are Informative

Techniques are informative—that means they are not required. The basis for determining conformance to WCAG 2.0 is the success criteria from the WCAG 2.0 standard—not the techniques. For important information about techniques, please see the Understanding Techniques for WCAG Success Criteria section of Understanding WCAG 2.0.