screen capture on ubuntu 14.04 (trusty thar)
list your pulse devices:
pactl list
record with avconf (which is a weird version of ffmpeg):
avconv -video_size 1024x768 -framerate 20 -b $((10*1024))k -f x11grab -i $DISPLAY -f pulse -ac 2 -i "alsa_input.usb-0b0e_Jabra_SPEAK_510_USB_1C48F9E60C09020A00-00-USB.analog-mono" -threads 2 -vcodec libx264 -acodec mp3 -preset ultrafast output.mp4