It currently takes at least a year before new software releases are sufficiently widely used that it is safe to depend on them. Any time you use any format other than plain text and standard HTML, you risk depriving users with disabilities from being able to use your site. This is one more reason to restrain use of multimedia to cases where it adds substantial value to a site. Deaf users can be supported by the use of captions on videos and transcripts of audio presentations. Such textual alternatives also make the content more accessible to search engines and facilitate translation.
Blind users are harder to support.
The traditional approach to making images accessible is to provide a textual description that can be read aloud by a talking browser, but doing so for a video can conflict with the audio track. For some videos, this may work. Other times, it may be necessary to provide a completely textual alternative that integrates the information found in the audio and visual tracks of the video. Many visually impaired users are not completely blind but do have reduced vision. Guidelines for multimedia on the Web .