ffmpeg -f x11grab -s 361x176 -framerate 25 -i :0.0 -pix_fmt yuv420p -vcodec libx264 /home/rabeet/Videos/output.mkv
ffmpeg version 2.4.3-1ubuntu1~trusty6 Copyright (c) 2000-2014 the FFmpeg developers
  built on Nov 22 2014 17:07:19 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  configuration: --prefix=/usr --extra-version='1ubuntu1~trusty6' --build-suffix=-ffmpeg --toolchain=hardened --extra-cflags= --extra-cxxflags= --libdir=/usr/lib/x86_64-linux-gnu --shlibdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --enable-shared --disable-stripping --enable-avresample --enable-avisynth --enable-fontconfig --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-opengl --enable-x11grab --enable-libxvid --enable-libx265 --enable-libdc1394 --enable-libiec61883 --enable-libzvbi --enable-libzmq --enable-frei0r --enable-libx264 --enable-libsoxr --enable-openal --enable-libopencv
  libavutil      54.  7.100 / 54.  7.100
  libavcodec     56.  1.100 / 56.  1.100
  libavformat    56.  4.101 / 56.  4.101
  libavdevice    56.  0.100 / 56.  0.100
  libavfilter     5.  1.100 /  5.  1.100
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  0.100 /  3.  0.100
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  0.100 / 53.  0.100
[x11grab @ 0x2360500] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 361 height: 176
[x11grab @ 0x2360500] shared memory extension found
Input #0, x11grab, from ':0.0':
  Duration: N/A, start: 1472649751.752386, bitrate: 50828 kb/s
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 361x176, 50828 kb/s, 25 tbr, 1000k tbn, 25 tbc
File '/home/rabeet/Videos/output.mkv' already exists. Overwrite ? [y/N] y
[libx264 @ 0x2382b00] width not divisible by 2 (361x176)
Output #0, matroska, to '/home/rabeet/Videos/output.mkv':
    Stream #0:0: Video: h264, q=2-31, 128 kb/s, 25 fps
    Metadata:
      encoder         : Lavc56.1.100 libx264
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height