X11 screencast (with audio)
Screenrecording of a 1024x768 pixel area, with an x/y-offset of 80/120px. Sound is recorded at a bitrate of 128kb/s from the analog input of the default ALSA sound card, the outline of the captured region is displayed on screen:
avconv -f x11grab -show_region 1 \
-s 1024x768 -i :0.0+80,120 \
-f alsa -i hw:0 \
-b:v 1200k -b:a 128k \
-y ~/screencast.mpg
Don't forget to check the mixer settings!
Recording sound from another application instead of an external source requires to modprobe the snd_aloop kernel module and a line of ALSA configuration:
### File: ~/.asoundrc
pcm.!default { type plug slave.pcm "hw:Loopback,0,0" }
Additionally, the avconv audio input parameters need to be changed to
-f alsa -i hw:Loopback,1,0
The configuration of an optional output channel for audio monitoring is described here at ffmpeg.org.