You could try recording it on the client side via something like RecordRTC.
Recording a MediaStream will be a standard feature available with the WebRTC APIs, but it has not yet been implemented: http://lists.w3.org/Archives/Public/public-media-capture/2013Jul/0049.html
We plan on adding support for recording to our API as well. Feel free to vote for it on our UserVoice page and add any comments on how you think it should work.