Microsoft UI Automation is a framework in Windows that provides information to assistive technologies.  Accessibility features related to video that can be tied into Silverlight through the UI Automation include captioning, tab sequences and high contrast themes.

Captioned videos for Silverlight can be produced through the Expression Encoder,  either as a limited free download a fully featured ‘Pro’ version.  The Microsoft Silverlight interface can support a variety of video formats and containers for captioned video.  The table below shows which formats are supported.

Delivery Method Supported Containers
Supported Containers by Delivery Method
Progressive download Windows Media, MP4, MP3, ASX
Windows Media Streaming over HTTP Windows Media, Server Side Play List (SSPL)
Smooth Streaming (specific type of MediaStreamSource) fMP4
ASX Windows Media, MP4, ASX
PlayReady DRM MP4
Server Side Playlist Windows Media
MediaStreamSource MediaStreamSourcegives the developer complete control over the container. Any container can be used as long as the developer writes or uses a parser for it.


Container Code
Windows Media
  • "353" - Microsoft Windows Media Audio v7 v8 and v9.x Standard (WMA Standard)
  • "354" - Microsoft Windows Media Audio v9.x and v10 Professional (WMA Professional)
  • WMV1 (Windows Media Video 7)
  • WMV2 (Windows Media Video 8)
  • WMV3 (Windows Media Video 9)
MP4 H.264 (ITU-T H.264 / ISO MPEG-4 AVC), AAC-LC
MP3 "85" - ISO MPEG-1 Layer III (MP3)


Additional information can be found on the Microsoft site including a Silverlight accessibility overview and information specially relating to the creation of audio and video.

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