Video works, but no audio in MCU room (it still works in P2P room)


I’ve installed the Licode in a fresh Ubuntu 14.04.
The weird thing is that only video works (I can see the webcam well on both
computer and android phone). However, there is no audio in MCU room.
I tried to switch to P2P room and both video & audio work fine.
I tried to see the log of erizoController, erizoAgent, but everything seems
During installation, I saw a lot of compiling warning for the libav*

Do you think it’s the root of the problem and what should I do to fix it?