RE: Captions for audio clips

I don't think the issue which Phill has raised arises under the current
guidelines. Checkpoint 1.3 refers only to the synchronization of auditory
descriptions with the audio track of an audio/visual presentation.
Checkpoint 1.4 is concerned with "time-based multimedia presentations",
such as "movies". A sound file is not a "multimedia" presentation, as the
term implies the involvement of more than one medium (stretching usage
somewhat one could argue that a sound file is a unimedia presentation).