This Web page lists SMIL Techniques from Techniques for WCAG 2.0: Techniques and Failures for Web Content Accessibility Guidelines 2.0. Technology-specific techniques do not replace the general techniques: content developers should consider both general techniques and technology-specific techniques as they work toward conformance.
Publication of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.0 success criteria and conformance requirements. Developers need to be aware of the limitations of specific technologies and provide content in a way that is accessible to people with disabilities.
For information about the techniques, see Introduction to Techniques for WCAG 2.0. For a list of techniques for other technologies, see the Table of Contents.
Applies whenever SMIL 1.0 player is available
This technique relates to:
The purpose of this technique is to allow there to be more audio description than will fit into the gaps in the dialogue of the audio-visual material.
With SMIL 1.0 there is no easy way to do this but it can be done by breaking the audio and video files up into a series of files that are played sequentially. Additional audio description is then played while the audio-visual program is frozen. The last frame of the video file is frozen so that it remains on screen while the audio file plays out.
The effect is that the video appears to play through from end to end but freezes in places while a longer audio description is provided. It then continues automatically when the audio description is complete.
To turn the extended audio description on and off one could use script to switch back and forth between two SMIL scripts, one with and one without the extended audio description lines. Or script could be used to add or remove the extended audio description lines from the SMIL file so that the film clips would just play sequentially.
If scripting is not available then two versions of the video could be provided, one with and one without extended audio descriptions.
Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns:qt="http://www.apple.com/quicktime/resources/smilextensions"
xmlns="http://www.w3.org/TR/REC-smil" qt:time-slider="true">
<head>
<layout>
<root-layout background-color="black" height="266" width="320"/>
<region id="videoregion" background-color="black" top="26" left="0"
height="144" width="320"/>
</layout>
</head>
<body>
<par>
<seq>
<par>
<video src="video.rm" region="videoregion" clip-begin="0s" clip-end="5.4"
dur="8.7" fill="freeze" alt="videoalt"/>
<audio src="no1.wav" begin="5.4" alt="audio alt"/>
</par>
<par>
<video src="video.rm" region="videoregion" clip-begin="5.4" clip-end="24.1"
dur="20.3" fill="freeze" alt="videoalt"/>
<audio src="no2.wav" begin="18.7" alt="audio alt"/>
</par>
<par>
<video src="video.rm" region="videoregion" clip-begin="24.1" clip-end="29.6"
dur="7.7" fill="freeze" alt="videoalt"/>
<audio src="no3.wav" begin="5.5" alt="audio alt"/>
</par>
<par>
<video src="video.rm" region="videoregion" clip-begin="29.6" clip-end="34.5"
dur="5.7" fill="freeze" alt="videoalt"/>
<audio src="no4.wav" begin="4.9" alt="audio alt"/>
</par>
<par>
<video src="video.rm" region="videoregion" clip-begin="77.4" alt="video alt"/>
</par>
</seq>
</par>
</body>
</smil>
The markup above is broken into five <par> segments. In each, there is a <video> and an <audio> tag (the last <par> has no <audio> tag intentionally). The convention with extended audio descriptions is that the main media pauses during the description. The way to make this happen in SMIL 1.0 is to set a "clip-begin" and "clip-end" which dictate the start and end of the video clip, and to set a duration for the clip that is longer than what is defined by the "clip-begin" and "clip-end". The fill="freeze" holds the last frame of the video during the extended description. The <audio> tag has a "begin" attribute with a value that is equal to the "clip-end" value of the preceding <video> tag.
To determine the values for "clip-begin," "clip-end", and "dur", find the start and end time of the portion of the video being described, and find out the total length of the extended audio description. The "clip-begin" and "clip-end" define their own values, but the "dur" value is the sum of the length of the extended description and the clip defined by the "clip-begin" and "clip-end". In the first <par>, the video clip starts at 0 seconds, ends at 5.4 seconds, and the description length is 3.3 seconds, so the "dur" value is 5.4s + 3.3s = 8.7s.
Resources are for information purposes only, no endorsement implied.
Play file with extended audio descriptions
Play file with audio description
Check whether video freezes in places and plays extended audio description
#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.
Applies whenever SMIL 2.0 player is available
This technique relates to:
The purpose of this technique is to allow there to be more audio description than will fit into the gaps in the dialogue of the audio-visual material.
With SMIL 2.0 it is possible to specify that particular audio files be played at particular times, and that the program be frozen (paused) while the audio file is being played.
The effect is that the video appears to play through from end to end but freezes in places while a longer audio description is provided. It then continues automatically when the audio description is complete.
To turn the extended audio description on and off one could use script to switch back and forth between two SMIL scripts, one with and one without the extended audio description lines. Or script could be used to add or remove the extended audio description lines from the SMIL file so that the film clips would just play uninterrupted.
If scripting is not available then two versions of the SMIL file could be provided, one with and one without extended audio description.
Example Code:
<smil xmlns="http://www.w3.org/2001/SMIL20/Language">
<head>
<layout>
<root-layout backgroundColor="black" height="266" width="320"/>
<region id="video" backgroundColor="black" top="26" left="0"
height="144" width="320"/>
</layout>
</head>
<body>
<excl>
<priorityClass peers="pause">
<video src="movie.rm" region="video" title="video" alt="video" />
<audio src="desc1.rm" begin="12.85s" alt="Description 1" />
<audio src="desc2.rm" begin="33.71s" alt="Description 2" />
<audio src="desc3.rm" begin="42.65s" alt="Description 3" />
<audio src="desc4.rm" begin="59.80s" alt="Description 4" />
</priorityClass>
</excl>
</body>
</smil> Resources are for information purposes only, no endorsement implied.
Play file with extended audio description
Check whether video freezes in places and plays extended audio description
#2 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.
Applies whenever SMIL 1.0 player is available
This technique relates to:
The objective of this technique is to provide a way for people who are blind or otherwise have trouble seeing the video in audio-visual material to be able to access the material. With this technique a description of the video is provided via audio description that will fit into the gaps in the dialogue in the audio-visual material.
Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns:qt="http://www.apple.com/quicktime/resources/smilextensions"
xmlns="http://www.w3.org/TR/REC-smil" qt:time-slider="true">
<head>
<layout>
<root-layout background-color="black" height="266" width="320"/>
<region id="videoregion" background-color="black" top="26" left="0"
height="144" width="320"/>
</layout>
</head>
<body>
<par>
<video dur="0:01:20.00" region="videoregion" src="salesdemo.mov"
alt="Sales Demo"/>
<audio dur="0:01:20.00" src="salesdemo_ad.mp3"
alt="Sales Demo Audio Description"/>
</par>
</body>
</smil> Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns="http://www.w3.org/TR/REC-smil">
<head>
<layout>
<root-layout background-color="black" height="266" width="320"/>
<region id="videoregion" background-color="black" top="26" left="0"
height="144" width="320"/>
</layout>
</head>
<body>
<par>
<video src="salesdemo.mov" region="videoregion" title="Sales Demo"
alt="Sales Demo"/>
<audio src="salesdemo_ad.mp3" title="audio description"
alt="Sales Demo Audio Description"/>
</par>
</body>
</smil>Resources are for information purposes only, no endorsement implied.
Find method for turning on audio description from content/player (unless it is always played by default)
Play file with audio description
Check whether audio description is played
#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.
Applies whenever SMIL 2.0 player is available
This technique relates to:
The objective of this technique is to provide a way for people who are blind or otherwise have trouble seeing the video in audio-visual material to be able to access the material. With this technique a description of the video is provided via audio description that will fit into the gaps in the dialogue in the audio-visual material.
Example Code:
<smil xmlns="http://www.w3.org/2001/SMIL20/Language">
<head>
<layout>
<root-layout backgroundColor="black" height="266" width="320"/>
<region id="video" backgroundColor="black" top="26" left="0"
height="144" width="320"/>
</layout>
</head>
<body>
<par>
<video src="salesdemo.mpg" region="video" title="Sales Demo"
alt="Sales Demo"/>
<audio src="salesdemo_ad.mp3" begin="33.71s" title="audio description"
alt="Sales Demo Audio Description"/>
</par>
</body>
</smil>
The example shows a <par> segment containing an <audio> and a <video> tag. The audio stream is not started immediately.
Resources are for information purposes only, no endorsement implied.
Find method for turning on audio description from content/player (unless it is always played by default)
Play file with audio description
Check whether audio description is played
#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.
Applies to SMIL 1.0
This technique relates to:
The objective of this technique is to provide a way for people who are deaf or otherwise have trouble hearing the dialogue in audio visual material to be able to view the material. With this technique all of the dialogue and important sounds are available in a text stream that is displayed in a caption area.
With SMIL 1.0, separate regions can be defined for the video and the captions. The captions and video playback are synchronized, with the caption text displayed in one region of the screen, while the corresponding video is displayed in another region.
Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns:qt="http://www.apple.com/quicktime/resources/smilextensions"
xmlns="http://www.w3.org/TR/REC-smil" qt:time-slider="true">
<head>
<layout>
<root-layout width="320" height="300" background-color="black"/>
<region top="0" width="320" height="240" left="0" background-color="black"
id="videoregion"/>
<region top="240" width="320" height="60" left="0" background-color="black"
id="textregion"/>
</layout>
</head>
<body>
<par>
<video dur="0:01:20.00" region="videoregion" src="salesdemo.mov"
alt="Sales Demo"/>
<textstream dur="0:01:20.00" region="textregion" src="salesdemo_cc.txt"
alt="Sales Demo Captions"/>
</par>
</body>
</smil> Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns="http://www.w3.org/TR/REC-smil">
<head>
<layout>
<root-layout background-color="black" height="310" width="330"/>
<region id="video" background-color="black" top="5" left="5"
height="240" width="320"/>
<region id="captions" background-color="black" top="250"
height="60" left="5" width="320"/>
</layout>
</head>
<body>
<par>
<video src="salesdemo.mpg" region="video" title="Sales Demo"
alt="Sales Demo"/>
<textstream src="salesdemo_cc.rt" region="captions"
system-captions="on" title="captions"
alt="Sales Demo Captions"/>
</par>
</body>
</smil> The example shows a <par> segment
containing a <video> and a
<code><![CDATA[<textstream> tag. The system-captions attribute indicates that the
textstream should be displayed when the user's player setting for
captions indicates the preference for captions to be displayed. The
<layout> section defines the regions
used for the video and the captions.
Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns="http://www.w3.org/TR/REC-smil">
<head>
<layout>
<root-layout background-color="black" height="310" width="330"/>
<region id="video" background-color="black" top="5" left="5"
height="240" width="320"/>
<region id="captions" background-color="black" top="250"
height="60" left="5" width="320"/>
</layout>
</head>
<body>
<par>
<video src="salesdemo.mpg" region="video" title="Sales Demo"
alt="Sales Demo"/>
<text src="data:,This%20is%20inline%20text." region="captions" begin="0s"
dur="3" alt="Sales Demo Captions">
<param name="charset" value="iso-8859-1"/>
<param name="fontFace" value="System"/>
<param name="fontColor" value="yellow"/>
<param name="backgroundColor" value="blue"/>
</text>
</par>
</body>
</smil>
This example shows a <text> element that
includes synchronized text streams within the SMIL file.
Resources are for information purposes only, no endorsement implied.
Enabled caption preference in player, if present
Play file with captions
Check whether captions are displayed
#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.
Applies to SMIL 2.0
This technique relates to:
The objective of this technique is to provide a way for people who are deaf or otherwise have trouble hearing the dialogue in audio visual material to be able to view the material. With this technique all of the dialogue and important sounds are available in a text stream that is displayed in a caption area.
With SMIL 2.0, separate regions can be defined for the video and the captions. The captions and video playback are synchronized, with the caption text displayed in one region of the screen, and the corresponding video displayed in another region.
Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns="http://www.w3.org/2001/SMIL20/Language">
<head>
<layout>
<root-layout backgroundColor="black" height="310" width="330"/>
<region id="video" backgroundColor="black" top="5" left="5"
height="240" width="320"/>
<region id="captions" backgroundColor="black" top="250"
height="60" left="5" width="320"/>
</layout>
</head>
<body>
<par>
<video src="salesdemo.mpg" region="video" title="Sales Demo"
alt="Sales Demo"/>
<textstream src="salesdemo_cc.rt" region="captions" systemCaptions="on"
title="captions" alt="Sales Demo Captions"/>
</par>
</body>
</smil>
The example shows a <par> segment
containing a <video> and a
<textstream> tag. The systemCaptions
attribute indicates that the textstream should be displayed when the
user's player setting for captions indicates the preference for
captions to be displayed. The <layout>
section defines the regions used for the video and the captions.
Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns="http://www.w3.org/2001/SMIL20/Language">
<head>
<layout>
<root-layout backgroundColor="black" height="310" width="330"/>
<region id="video" backgroundColor="black" top="5" left="5"
height="240" width="320"/>
<region id="captions" backgroundColor="black" top="250"
height="60" left="5" width="320"/>
</layout>
</head>
<body>
<par>
<video src="salesdemo.mpg" region="video" title="Sales Demo"
alt="Sales Demo"/>
<text src="data:,This%20is%20inline%20text." region="captions"
begin="0s" dur="3">
<param name="charset" value="iso-8859-1"/>
<param name="fontFace" value="System"/>
<param name="fontColor" value="yellow"/>
<param name="backgroundColor" value="blue"/>
</text>
<text src="data:,This%20is%20a%20second%20text."
region="captions" begin="3s" dur="3">
<param name="charset" value="iso-8859-1"/>
<param name="fontFace" value="System"/>
<param name="fontColor" value="yellow"/>
<param name="backgroundColor" value="blue"/>
</text>
</par>
</body>
</smil>
This example shows a <text> element that
includes synchronized text streams within the SMIL file.
Resources are for information purposes only, no endorsement implied.
Enabled caption preference in player, if present
Play file with captions
Check whether captions are displayed
#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.
Applies whenever SMIL 1.0 player is available
This technique relates to:
The objective of this technique is to provide a way for people who are deaf or otherwise have trouble hearing the dialogue in audio visual material to be able to view the material. With this technique all of the dialogue and important sounds are available in a sign-language interpretation video that is displayed in a caption area.
With SMIL 1.0, separate regions can be defined for the two videos. The two video playbacks are synchronized, with the content video displayed in one region of the screen, while the corresponding sign-language interpretation video is displayed in another region.
Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns:qt="http://www.apple.com/quicktime/resources/smilextensions"
xmlns="http://www.w3.org/TR/REC-smil" qt:time-slider="true">
<head>
<layout>
<root-layout width="320" height="300" background-color="black"/>
<region top="0" width="320" height="240" left="0" background-color="black"
id="videoregion"/>
<region top="240" width="320" height="60" left="0" background-color="black"
id="signingregion"/>
</layout>
</head>
<body>
<par>
<video dur="0:01:20.00" region="videoregion" src="salesdemo.mov"
alt="Sales Demo"/>
<video dur="0:01:20.00" region="signingregion" system-captions="on"
src="salesdemo_si.mov" alt="Sales Demo Sign Language Interpretation"/>
</par>
</body>
</smil>Example Code:
<?xml version="1.0" encoding="UTF-8"?>
<smil xmlns="http://www.w3.org/TR/REC-smil">
<head>
<layout>
<root-layout background-color="black" height="310" width="330"/>
<region top="0" width="320" height="240" left="0" background-color="black"
id="videoregion"/>
<region top="240" width="320" height="60" left="0" background-color="black"
id="signingregion"/>
</layout>
</head>
<body>
<par>
<video dur="0:01:20.00" region="videoregion" src="salesdemo.mov"
alt="Sales Demo"/>
<video dur="0:01:20.00" region="signingregion" system-captions="on"
src="salesdemo_si.mov" alt="Sales Demo Sign Language Interpretation"/>
</par>
</body>
</smil> The example shows a <par> segment
containing two <video> tags. The
system-captions attribute indicates that the sign language video
should be displayed when the user's player setting for captions
indicates the preference for captions to be displayed. The
<layout> section defines the regions
used for the main video and the sign language interpretation video.
Resources are for information purposes only, no endorsement implied.
Enable control in content or player to turn on sign language interpretation (unless it is always shown)
Play file with sign-language interpretation
Check whether sign language interpretation is displayed
#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.
SMIL 2.0
This technique relates to:
The objective of this technique is to provide a way for people who are deaf or otherwise have trouble hearing the dialogue in audio visual material to be able to view the material. With this technique all of the dialogue and important sounds are available in a sign-language interpretation video that is displayed in a caption area.
With SMIL 2.0, separate regions can be defined for the two videos. The two video playbacks are synchronized, with the content video displayed in one region of the screen, while the corresponding sign-language interpretation video is displayed in another region.
Example Code:
<smil xmlns="http://www.w3.org/2001/SMIL20/Language">
<head>
<layout>
<root-layout backgroundColor="black" height="310" width="330"/>
<region id="video" backgroundColor="black" top="5" left="5"
height="240" width="320"/>
<region id="signing" backgroundColor="black" top="250"
height="60" left="5" width="320"/>
</layout>
</head>
<body>
<par>
<video src="salesdemo.mpg" region="video" title="Sales Demo"
alt="Sales Demo"/>
<video src="salesdemo_signing.mpg"
region="signing" systemCaptions="on"
title="sign language interpretation"
alt="Sales Demo Sign Language Interpretation"/>
</par>
</body>
</smil>
The example shows a <par> segment containing
two <video> tags. The systemCaptions
attribute indicates that the sign language video should be displayed
when the user's player setting for captions indicates the preference
for captions to be displayed. The <layout>
section defines the regions used for the main video and the sign
language interpretation video.
Resources are for information purposes only, no endorsement implied.
Enable control in content or player to turn on sign language interpretation (unless it is always shown)
Play file with sign-language interpretation
Check whether sign language interpretation is displayed
#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.