transcoding

 $ ffmpeg -f lavfi -i testsrc -t 1 -c:v libx264 -y test.mkv -loglevel error && ./doc/examples/transcoding test.mkv out.mkv 
Input #0, matroska,webm, from 'test.mkv':
  Metadata:
    ENCODER         : Lavf57.23.101
  Duration: 00:00:01.00, start: 0.000000, bitrate: 68 kb/s
    Stream #0:0: Video: h264 (High 4:4:4 Predictive), yuv444p, 320x240 [SAR 1:1 DAR 4:3], 25 fps, 25 tbr, 1k tbn, 50 tbc (default)
    Metadata:
      ENCODER         : Lavc57.24.101 libx264
      DURATION        : 00:00:01.000000000
[libx264 @ 0xa067d0] broken ffmpeg default settings detected
[libx264 @ 0xa067d0] use an encoding preset (e.g. -vpre medium)
[libx264 @ 0xa067d0] preset usage: -vpre <speed> -vpre <profile>
[libx264 @ 0xa067d0] speed presets are listed in x264 --help
[libx264 @ 0xa067d0] profile is optional; x264 defaults to high
Cannot open video encoder for stream #0
Error occurred: Generic error in an external library
[ERR]
18:47:45j@zver /src/ffmpeg
 $ git describe
n2.9-dev-3343-gae5b2c5
[OK]