ffmpeg -f x11grab -video_size 1600x900 -framerate 30 -i :0.0 -f v4l2 -video_size 320x240 \
  -framerate 30 -i /dev/video0 -input_format yuyv422 -f alsa -ac 2 -i plughw:0,0 -filter_complex \
   "[0:v]scale=1024:-1,setpts=PTS-STARTPTS[bg];[1:v]scale=120:-1,setpts=PTS-STARTPTS[fg];[bg][fg]overlay=10:H-h-10,format=yuv420p[out]" \
  -map "[out]" -map 2:a -vcodec libx264 -maxrate 3000k -bufsize 4000k -g 2 \
  -acodec libmp3lame -ar 44100 -b:a 128k -f flv $STREAM_URL

[moe@marvin ~]$ ./test.sh
ffmpeg version 2.1.3 Copyright (c) 2000-2013 the FFmpeg developers
  built on Jan 15 2014 20:51:13 with gcc 4.8.2 (GCC) 20131219 (prerelease)
  configuration: --prefix=/usr --disable-debug --disable-static --enable-avresample --enable-dxva2 --enable-fontconfig --enable-gnutls --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libv4l2 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-pic --enable-postproc --enable-runtime-cpudetect --enable-shared --enable-swresample --enable-vdpau --enable-version3 --enable-x11grab
  libavutil      52. 48.101 / 52. 48.101
  libavcodec     55. 39.101 / 55. 39.101
  libavformat    55. 19.104 / 55. 19.104
  libavdevice    55.  5.100 / 55.  5.100
  libavfilter     3. 90.100 /  3. 90.100
  libavresample   1.  1.  0 /  1.  1.  0
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
[x11grab @ 0x7ebca0] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 1600 height: 900
[x11grab @ 0x7ebca0] shared memory extension found
Input #0, x11grab, from ':0.0':
  Duration: N/A, start: 1392004435.484551, bitrate: 1382400 kb/s
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1600x900, 1382400 kb/s, 30 tbr, 1000k tbn, 30 tbc
Input #1, video4linux2,v4l2, from '/dev/video0':
  Duration: N/A, start: 120600.081305, bitrate: 36864 kb/s
    Stream #1:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 320x240, 36864 kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
Option input_format not found.