recording the output of the Web Audio API

Apologies for the naive question (as I'm pretty sure it must have been
discussed already) but is there a currently available method for exporting
the output of the Web Audio API to a downloadable file (e.g. WAV/MP3)? My
first thought was the Media Capture/Streams API, but I'm not sure if the
capability is there yet.

Also it would be great if we could prompt the user to download a file via
solely client-side processing, without having to stream the audio to a
server and package the download there. Not sure if either of these are
possible scenarios right now though.

Matt