TVideos require three things to be accessible:
a video player that is keyboard accessible
You must provide the first two, the third is covered by the standard player used in the various platforms.
Audio and video transcripts are helpful to a number of different populations—those with hearing impairments, vision impairments, cognitive learning disabilities, and ESL users.
Students with hearing impairments need a caption/transcript for the audio component of a video.
Students with vision impairments need a transcript for the visual component of a video.
Students with various cognitive learning disabilities may benefit from a caption/transcript.
Students who are non-native English speakers may find a caption/transcript helpful in following the audio portion of a video.
Web accessibility requires a transcript for all videos linked on the web page. Captions provide a transcript of any audio in a video within the video player. Unlike a transcript, the caption does not provide a description of the visual elements in the video. Captions are helpful by providing the audio information for those who need it without the need for opening/downloading an additional document. Captions may be open (built into the video file and always displayed) or closed (user can turn the captions on or off).
The standard is to provide both a transcript and closed captions for all videos.
the text of the audio information for hearing impaired users outside of the video player (also helpful for non-native speakers and those with some learning disabilities)
narrative of the visual elements not already included in the audio transcript for visually impaired users
Closed captions provide:
text of the audio information for hearing impaired users within the video player (also helpful for non-native speakers and those with some learning disabilities)