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ffmpeg -video_size 1600x900 -framerate 60 -f x11grab -i :0.0+0,0 output1.mp4
ffmpeg version 2.6.3 Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 4.8.2 (GCC)
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --docdir=/usr/doc/ffmpeg-2.6.3/html --mandir=/usr/man --disable-debug --enable-shared --disable-static --enable-pthreads --enable-libtheora --enable-libvorbis --enable-gpl --enable-version3 --enable-postproc --enable-swscale --enable-x11grab --enable-avfilter --enable-gnutls --enable-libcdio --enable-libssh --enable-libcaca --enable-libsmbclient --enable-opengl --arch=x86_64 --enable-libmp3lame --enable-libxvid --enable-libx264
  libavutil      54. 20.100 / 54. 20.100
  libavcodec     56. 26.100 / 56. 26.100
  libavformat    56. 25.101 / 56. 25.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 11.102 /  5. 11.102
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
[x11grab @ 0x1e00640] Capture area 1600x900 at position 0.0 outside the screen size 1600x900
:0.0+0,0: Invalid argument