sergio@sergio-desktop:~/ffmpeg-git-20151106-64bit-static$ ./ffmpeg -video_size 700x420 -framerate 10 -f x11grab -i :0.0+50,0 -ab 96k -ar 44100 -b 345k -c:v libx264 test2.mkv
ffmpeg version N-50966-gc878082-static http://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 5.2.1 (Debian 5.2.1-23) 20151028
  configuration: --enable-gpl --enable-version3 --disable-shared --disable-debug --enable-runtime-cpudetect --enable-libmp3lame --enable-libx264 --enable-libx265 --enable-libwebp --enable-libspeex --enable-libvorbis --enable-libvpx --enable-libfreetype --enable-fontconfig --enable-libxvid --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-gray --enable-libopenjpeg --enable-libopus --enable-libass --enable-gnutls --enable-libvidstab --enable-libsoxr --enable-frei0r --enable-libfribidi --disable-indev=sndio --disable-outdev=sndio --cc=gcc
  libavutil      55.  5.100 / 55.  5.100
  libavcodec     57. 14.100 / 57. 14.100
  libavformat    57. 14.100 / 57. 14.100
  libavdevice    57.  0.100 / 57.  0.100
  libavfilter     6. 14.101 /  6. 14.101
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.100 /  2.  0.100
  libpostproc    54.  0.100 / 54.  0.100
Input #0, x11grab, from ':0.0+50,0':
  Duration: N/A, start: 1446828421.344520, bitrate: N/A
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 700x420, 10 fps, 10 tbr, 1000k tbn, 10 tbc
Please use -b:a or -b:v, -b is ambiguous
No pixel format specified, yuv444p for H.264 encoding chosen.
Use -pix_fmt yuv420p for compatibility with outdated media players.
[libx264 @ 0x5102760] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0x5102760] profile High 4:4:4 Predictive, level 2.2, 4:4:4 8-bit
[libx264 @ 0x5102760] 264 - core 148 r209 7599210 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=10 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=abr mbtree=1 bitrate=345 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, matroska, to 'test2.mkv':
  Metadata:
    encoder         : Lavf57.14.100
    Stream #0:0: Video: h264 (libx264) (H264 / 0x34363248), yuv444p, 700x420, q=-1--1, 345 kb/s, 10 fps, 1k tbn, 10 tbc
    Metadata:
      encoder         : Lavc57.14.100 libx264
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Press [q] to stop, [?] for help
frame=   40 fps=9.8 q=-1.0 Lsize=     141kB time=00:00:03.80 bitrate= 304.4kbits/s
video:140kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.692854%
[libx264 @ 0x5102760] frame I:1     Avg QP:20.37  size: 60059
[libx264 @ 0x5102760] frame P:14    Avg QP:23.14  size:  5811
[libx264 @ 0x5102760] frame B:25    Avg QP:32.27  size:    60
[libx264 @ 0x5102760] consecutive B-frames: 15.0%  0.0% 15.0% 70.0%
[libx264 @ 0x5102760] mb I  I16..4: 16.8% 14.5% 68.7%
[libx264 @ 0x5102760] mb P  I16..4:  0.7%  0.3%  4.7%  P16..4:  7.3%  1.3%  0.9%  0.0%  0.0%    skip:84.7%
[libx264 @ 0x5102760] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  1.4%  0.0%  0.0%  direct: 0.0%  skip:98.5%  L0:13.7% L1:86.3% BI: 0.0%
[libx264 @ 0x5102760] final ratefactor: 20.91
[libx264 @ 0x5102760] 8x8 transform intra:10.8% inter:54.6%
[libx264 @ 0x5102760] coded y,u,v intra: 55.5% 13.5% 13.0% inter: 1.4% 0.7% 0.7%
[libx264 @ 0x5102760] i16 v,h,dc,p: 35% 62%  2%  0%
[libx264 @ 0x5102760] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 73%  6% 19%  0%  1%  0%  0%  0%  1%
[libx264 @ 0x5102760] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 39% 28% 10%  2%  4%  4%  4%  4%  5%
[libx264 @ 0x5102760] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x5102760] ref P L0: 82.3%  6.3%  8.8%  2.6%
[libx264 @ 0x5102760] ref B L0: 85.5% 14.5%
[libx264 @ 0x5102760] ref B L1: 91.9%  8.1%
[libx264 @ 0x5102760] kb/s:285.81
Exiting normally, received signal 2.