Multimedia presentations can enrich education and enhance learning for many students, but it can also pose barriers for others. Audio and video are inaccessible to people who are unable to hear, and video is inaccessible to people who are unable to see critical information that is presented visually. Other students are impacted by low bandwidth Internet connections. Multimedia players can pose barriers as well if the player controls require use of a mouse or if they are not labeled sufficiently to be usable by screen reader users.
To address the needs of students who are unable to hear the audio, a transcript is an adequate accommodation for an audio recording or podcast. A transcript is also an important alternative to video for people with low bandwidth connections, as well as people who are unable to see or hear the content and who therefore would be unable to access captions (they can read the transcript using assistive technologies such as Braille output devices).
However, for most people who are unable to hear a video, a transcript does not provide an equivalent experience. The presentation's message is dependent on the simultaneous interaction between its audio and video portions. Even in simple lectures, much of the message is presented through the lecturer's nonverbal communication. For this reason, video should be captioned. Fortunately, it is very easy to create captions from a transcript. The transcript simply needs to be organized into short caption-sized segments (e.g., sentences or phrases) and timestamped. A wide variety of free tools are available that perform that function, including some that do it automatically (e.g., YouTube).
Captions can either be open (part of the video display, therefore always on) or closed (contained within a separate text track, synchronized with the video by the video player). Most media players, including web-based and standalone software players, support closed captions. However, some do not, so support for closed captions is a very important consideration when choosing which media player to use for delivering your content.
A variety of free tools have been developed that support the creation of transcripts and closed captions, motivated in part by YouTube's support for closed captions. The following is a list of some of these tools:
- Amara  (formerly Universal Subtitles)
- dotSub 
- Subtitle Horse 
- CaptionTube 
- MAGpie 
- Subtitle Workshop 
- World Caption
- Easy YouTube Caption Creator
There are also several vendors that specialize in high volume captioning services for enterprise clients. Some of these vendors offer robust services including seamless integration with YouTube, iTunes, and lecture capture systems. Examples include:
Additional information about multimedia accessibility is provided in the following Knowledge Base articles:
- What types of closed caption files do video players support?
- What is the difference between open and closed captioning?
- What is audio description?
- What standards exist for developing and purchasing accessible video and multimedia products?
- How can educational entities plan an accessible video production?
- Does making our school web content accessible mean I cannot use multimedia on my site?
- DO-IT: A Promising Practice in Delivering Accessible Video
- NAD: A Promising Practice in Streaming Captioned Educational Video
-  Amara
-  dotSub
-  Subtitle Horse
-  CaptionTube
-  MAGpie
-  Subtitle Workshop