Recording file has no sound

Hi all,
when i try to record streams; the mkv file i get has no audio. But my stream has no problem with audio.
my localstream config is;
var config = {
audio: true,
video: true,
videoSize: [640, 480, 640, 480],
videoFrameRate: [10, 20],
attributes: { username: “” + user_id }

what audio and video codecs are you using?

i am using default settings so it should be “vp8” video codec “opus” audio codec.
And also i forgot to mention i am testing this on newly install ubuntu 14.04 server in the VMware workstation.