title: ffmpeg "Requested output format 'decklink is not a suitable format'"
body: <p>I am trying to play a video using ffmpeg and decklink.
  I compiled ffmpeg from ffmpeg repo.
  I am working in ubuntu 16.04 lts.</p>
  
  <p>Here is my command : </p>
  
  <pre><code>./ffmpeg -err_detect ignore_err -threads 0 -re -i ./sample_1080_50i.ts -bufsize 1M -vf yadif -format_code Hi50 -f decklink -preroll 0.7 -pix_fmt uyvy422 'DeckLink Studio 4K'
  </code></pre>
  
  <p>The result is : </p>
  
  <pre><code>ffmpeg version N-89978-gcb97400 Copyright (c) 2000-2018 the FFmpeg developers
    built with gcc 5.1.1 (Ubuntu 5.1.0-0ubuntu11~10.04.2)
    configuration: --prefix=/home/sarslan/ffmpeg_build --pkg-config-flags=--static --extra-cflags='-I/home/sarslan/ffmpeg_build/include -I/home/sarslan/ffmpeg_sources/Blackmagic_DeckLink_SDK_10.9.5/Linux/include' --extra-ldflags=-L/home/sarslan/ffmpeg_build/lib --extra-libs='-lpthread -lm' --bindir=/home/sarslan/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree --enable-static --disable-shared --enable-decklink --enable-ffplay
    libavutil      56.  7.100 / 56.  7.100
    libavcodec     58. 10.100 / 58. 10.100
    libavformat    58.  9.100 / 58.  9.100
    libavdevice    58.  1.100 / 58.  1.100
    libavfilter     7. 11.101 /  7. 11.101
    libswscale      5.  0.101 /  5.  0.101
    libswresample   3.  0.101 /  3.  0.101
    libpostproc    55.  0.100 / 55.  0.100
  Input #0, mpegts, from './sample_1080_50i.ts':
    Duration: 00:05:00.08, start: 1.437333, bitrate: 4675 kb/s
    Program 1 
      Metadata:
        service_name    : Service01
        service_provider: FFmpeg
      Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 25 tbr, 90k tbn, 50 tbc
      Stream #0:1[0x101](eng): Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, stereo, fltp, 123 kb/s
  [NULL @ 0xb2ed180] Requested output format 'decklink' is not a suitable output format
  DeckLink Studio 4K: Invalid argument
  </code></pre>
  
  <p>I think, this error is weird.
  I enabled decklink support with --enable-decklink, and I also check ffmpeg documentation decklink part.'decklink' is used with -f option in every example. </p>
  
  <p>Then I check the command line, and I can't find any error with the command.
  Do you have any idea what the problem is?</p>
  
  <p>Thanks and best regards,</p>