The Microsoft Accessibility Team
September 1998
Authors of Web pages and multimedia software titles can now add closed captioning for users who are deaf or hard-of-hearing.
The technology for adding the closed captioning—Microsoft® Synchronized Accessible Media Interchange (SAMI)—was released this summer along with Microsoft's new Windows® Media Player.
SAMI will simplify captioning for developers and help expand access for end users.
Closed captioning was initially developed by public TV station WGBH in Boston for the estimated 20 million Americans who are deaf or hard-of-hearing. Now, with SAMI, this ability is available to a wide range of multimedia products, including Web-based products.
Advantages of SAMIThe SAMI technology creates a captioning file that is time-synchronized to a multimedia source file—audio, video, or animation. The source file is played through Windows Media Player on the Windows 98, Windows 95, or Windows NT® version 4.0 operating systems. (A beta version of Windows Media Player is also available for Windows 3.x.) Media Player then synchronizes the captioning to the source file, providing closed captioning.
Because this new method of closed captioning places the caption information in a separate file from the media file, caption and media content can be developed and distributed independently. Previously, content providers had to include the caption information within the media file, making it difficult to add captions after the fact, to correct mistakes, or to provide captions for additional languages.
Users will have great flexibility to adjust the appearance and presentation of captions to suit their needs and preferences. For instance, users can adjust the color, size, and font used for captions, as well as the background color.
Architectural OverviewThe new caption technology consists of the following data formats and components:
SAMI format. A content provider uses the SAMI format to create a file with caption information. The SAMI format is modeled after basic HTML and cascading style sheets. This format can store multiple versions of captioning information. For example, a single SAMI file can contain captions in several presentation styles and foreign languages.
To synchronize the captions with a media presentation, the captioning information in a SAMI file is associated with timestamps. The timestamps indicate the point in the media presentation (elapsed time into the show) at which to display the associated captioning.
Windows Media Player. The media player on the client's desktop synchronizes the captioning information in a SAMI document with the media file. The new Windows Media Player replaces ActiveMovie™, DirectShow™, and NetShow™.
Windows Media Player consists of a file reader that sends media data to a series of COM-based programs called filters. Each filter processes a specific type of media data, such as audio or video. To make Media Player work with SAMI, a new filter for SAMI data was created.
The multimedia title author or Web page author creates a SAMI document for each piece of media. Then he or she simply loads both the media file and the SAMI file into Windows Media Player.
To learn more about Windows Media Player, see www.microsoft.com/windows/mediaplayer/.
Client-side SAMI rendering engine. SAMI files, like HTML files, must be rendered for display on the client machine. At appropriate points in the media presentation, the SAMI filter in Media Player posts the caption data. The captions can be obtained programmatically or rendered by the Windows Media Player if Microsoft Internet Explorer 4.0 or Windows 98 is installed. (SAMI is not compatible with earlier versions of Internet Explorer or with any versions of Netscape or other browsers.)
Free to DevelopersThe SAMI file format specification is being made available to the public as an "open" (no licensing fees) standard. There are specifications, demos, and examples on Microsoft's Accessibility Web site at www.microsoft.com/enable/.