Per discussion at Audio WG f2f 2013-03-26
"Audio file data can be in any of the formats supported by the audio element"
"...can be accepted in formats containing only audio data (w/o video)"
This is to avoid the overhead of dealing with video containers that have an audio track.
What's the downside of supporting media formats that contain video tracks? I think in our implementation there's no implementation cost to supporting all the formats our HTML media elements support.
Web Audio API issues have been migrated to Github.
Closing. See https://github.com/WebAudio/web-audio-api/issues for up to date list of issues for the Web Audio API.