- Important note: This Wiki page is edited by participants of the User Agent Accessibility Guidelines working group (UAWG). It does not necessarily represent consensus and it may have incorrect information or information that is not supported by other Working Group participants, WAI, or W3C. It may also have some very useful information.
- 1 Guideline 2.11 (was 2.9)
- 1.1 2.11.1 Background Image Toggle
- 1.2 2.11.2 Time-Based Media Load-Only
- 1.3 2.11.5 Playback Rate Adjustment for Prerecorded Content
- 1.4 2.11.6 Stop/Pause/Resume Time-Based Media
Guideline 2.11 (was 2.9)
Guideline 2.11 Provide control of content that may reduce accessibility.
2.11.1 Background Image Toggle
2.11.1 (former 4.9.1) Background Image Toggle: The user has the global option to hide/show background images. (Level A)
Users can have difficulty reading text or recognizing images that are shown against variable backgrounds. Background images can also be distracting, especially to some people with cognitive impairments.
- John finds multiple images behind the text he is reading distracting. He navigates to his favorite news site where he finds today's weather displayed over a picture of a sunny sky with fluffy clouds. He activates a button on a toolbar named "Hide Background" and now can easily determine he's in for a day filled with sunshine.
- Sasha requires high contrast to be able to discriminate the shape of letters. She always sets a preference in her browser to turn off background images, so that she can see the text clearly without the variations in the background.
1.1.1 Configure Default Rendering allows the user to hide foreground images by replacing them with alternative content, but 2.9.1 extends this to background images in languages such as HTML that do not support alternative content for background images.
2.11.2 Time-Based Media Load-Only
2.11.2 (former 4.9.2) Time-Based Media Load-Only: The user can load time-based media content @@ Editors' Note: DEFINE@@ such that the first frame is displayed (if video), but the content is not played until explicit user request. (Level A)
Users should be in control of whether media plays automatically because it can interfere with assistive technology, be a distraction to themselves or to other users in the vicinity, or start content that would be harmful to users with seizure disorders.
- Jill browses browses the web using a screen reader to listen to the text of web pages. She navigates to her favorite shopping site and is greeted with trumpets blaring and an announcer shouting "Sale, sale, sale!" The audio is so loud that she can no longer hear the web page content. Jill closes her browser and changes a setting titled Play Audio on Request to yes and visits her shopping site again. This time she can read the content and when she is ready plays the audio and smiles, thinking of the deal's she is about to find.
- Jamie has epilepsy that's triggered by certain types of audio. She sets browser so that content does not play automatically so she can avoid audio that could trigger her epilepsy.
- Kendra has photo-epilepsy. She sets her browser so that content does not play automatically so she can avoid flashing content that could trigger her photo epilepsy.
- Guideline 2.4 Help users avoid flashing that could cause seizures.
2.11.5 Playback Rate Adjustment for Prerecorded Content
2.11.5 Playback Rate Adjustment for Prerecorded Content: The user can adjust the playback rate of prerecorded time-based media content, such that all of the following are true (Level A):
- The user can adjust the playback rate of the time-based media tracks to between
50% and 250% of real time.
- Speech whose playback rate has been adjusted by the user maintains pitch in order to
limit degradation of the speech quality.
- Audio and video tracks remain synchronized across this required
range of playback rates.
- The user agent provides a function that resets
the playback rate to normal (100%).
Users with sensory and cognitive impairments may have difficulty following or understanding spoken audio when presented at the normal playback rate. By slowing down the audio presentation of speech, while maintaining the pitch, or frequency characteristics, users are better able to follow the spoken content. For users with visual impairments familiar with the speeding up of speech presentation using screen readers or digital audio book players, the ability to speed up the audio, while maintaining pitch, allows those users to skim spoken audio without loss of understandability of the speech. Users with learning disabilities may be distracted or otherwise unable to follow complex animations or instructional video. By allowing the presentation to be slowed, the user has a better opportunity to observe the visual events of the animation. Additionally, a person may want to slow down the media if they are trying to take notes, and do so slowly because of language or dexterity impairments, etc.
Timo experienced a traumatic brain injury and has difficulty in comprehending speech. When listening to episodes of his favorite podcast on the Web, he slows down the audio by 50% and is able to understand the interviewer's and guest's question and answer session.
Anu is a blind university student who has grown up with digital talking book players, and regularly listens to spoken audio at 200% of normal speaking rate. In studying for exams, she reviews the online lecture videos from her History course, adjusting the presentation rate to 2x on the Web video player, in order to quickly review the material, and slowing the presentation down to normal rate when she encounters material she needs to review carefully.
Perttu has a learning disability and requires a longer time to follow instructions. He likes to cook and is watching a cooking demonstration on the Web. The instructions go by too quickly, and Perttu slows the video player to half speed in order to make it easier to follow the recipe being prepared.
2.11.6 Stop/Pause/Resume Time-Based Media
The user can stop, pause, and resume rendered audio and animation content (including video and animated images) that last three or more seconds at their default playback rate. (Level A)
Time-based media may contain information in visual and auditory modalities that can require additional time to recognize or understand by users with sensory or cognitive impairments. Users of screen readers that produce synthetic speech can experience difficulty when there is ongoing audio within time-based media, making it hard for the user to explore controls or other textual content related to the media presentation if the audio interferes with the speech synthesizer. In both instances, the ability to stop, pause and resume time-based media presentation is essential, allowing the user time to understand time-based content or examine content without interference with assistive technologies.
Proposed changes for clarity:
Time-based media may contain information in visual and auditory modalities that require users with sensory or cognitive impairments to take additional time to recognize or understand. Screen reader users can experience difficulty in audio within time-based media interferes with the speech produced by the screen reader. It is difficult for the user to explore controls or other textual content related to the media presentation if the audio interferes with the speech synthesizer. In both instances, the ability to stop, pause and resume time-based media presentation is essential, allowing the user time to understand time-based content or examine content without interference with assistive technologies.
Small adjustments to the proposed change:
Time-based media may contain information in visual and auditory modalities that requires additional time for users with sensory or cognitive impairments to recognize or understand. Screen reader users can experience difficulty with audio within time-based media that interferes with the speech produced by the screen reader. It is difficult for the user to explore controls or other textual content related to the media presentation if the audio interferes with the speech synthesizer. In both instances, the ability to stop, pause and resume time-based media presentation is essential, allowing the user time to understand time-based content or examine content without interference with assistive technologies.
Users with sensory or cognitive impairments may need extra time to recognize and understand the information, particularly in some time-based media. In addition, audio content can make it difficult for users to hear the synthesized speech from their screen reader utilities, and those same utilities can also be overwhelmed or confused by rapidly changing visual content. In these cases the ability to stop, pause, and resume time-based media presentation allows the user time to understand time-based content and other content around it without the time-based media interfering with their assistive technologies.
Claus has an attention deficit disorder and finds it difficult to follow instructional videos provided as part of his Web-based biology course. The videos incorporate text instructions that appear at key points, which are not displayed long enough for Claus to read them. Using the Web browser's built in media controls, Claus can pause the video when the instructions appear, and have as much time as needed to read and understand them before resuming the video playback.
Christine is a blind technology consultant and she regularly listens to podcasts about emerging Web technologies. One of her favorite podcasters augments the audio presentation with pop-up text boxes containing URLs or other useful information concerning the topic being presented. Christine likes the fact that her screen reader announces the presence of the pop-ups and begins reading the content, but the speech synthesizer interferes with the ongoing speech in the podcast. Using the media player pause command, Christine can easily stop the playback, allowing her to read the pop-up text, and then resume playback when she is ready.