['/usr/local/bin/ffmpeg', '-f', 'image2', '-framerate', '1/5', '-i', 'test_rand/11-small.png', '-f', 'image2', '-framerate', '1/5', '-i', 'test_rand/25-small.png', '-f', 'image2', '-framerate', '1/5', '-i', 'test_rand/25-small.png', '-filter_complex', 'concat=n=3:v=1:a=0,fps=1/5', '-vcodec', 'mpeg4', '-b:v', '800k', '-f', 'matroska', '-y', 'pipe:1']
-----------------
ffmpeg version 2.4.3 Copyright (c) 2000-2014 the FFmpeg developers
  built on Nov  6 2014 23:40:10 with Apple LLVM version 6.0 (clang-600.0.54) (based on LLVM 3.5svn)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/2.4.3 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --enable-avresample --enable-vda --cc=clang --host-cflags= --host-ldflags= --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libxvid
  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
Input #0, image2, from 'test_rand/11-small.png':
  Duration: 00:00:05.00, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: png, rgb24, 240x80, 0.20 tbr, 0.20 tbn, 0.20 tbc
Input #1, image2, from 'test_rand/25-small.png':
  Duration: 00:00:05.00, start: 0.000000, bitrate: N/A
    Stream #1:0: Video: png, rgb24, 240x80, 0.20 tbr, 0.20 tbn, 0.20 tbc
Input #2, image2, from 'test_rand/25-small.png':
  Duration: 00:00:05.00, start: 0.000000, bitrate: N/A
    Stream #2:0: Video: png, rgb24, 240x80, 0.20 tbr, 0.20 tbn, 0.20 tbc
[mpeg4 @ 0x7faae4045200] too many threads/slices (6), reducing to 5
Output #0, matroska, to 'pipe:1':
  Metadata:
    encoder         : Lavf56.4.101
    Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 240x80, q=2-31, 800 kb/s, 0.20 fps, 1k tbn, 0.20 tbc (default)
    Metadata:
      encoder         : Lavc56.1.100 mpeg4
Stream mapping:
  Stream #0:0 (png) -> concat:in0:v0
  Stream #1:0 (png) -> concat:in1:v0
  Stream #2:0 (png) -> concat:in2:v0
  fps -> Stream #0:0 (mpeg4)
Press [q] to stop, [?] for help
frame=    1 fps=0.0 q=2.5 Lsize=       4kB time=00:00:05.00 bitrate=   7.4kbits/s
video:4kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 16.350290%