title: Not able to pipe gstreamer output into ffmpeg
body: <p>has anybody gotten gstreamer to successfully pipe it's video output into ffmpeg?</p>
  
  <p>I've tried playing with /dev/stdout and I keep getting errors:</p>
  
  <p>gst-launch -e v4l2src device=/dev/video0 ! 'video/x-raw-yuv,width=1920,height=1080,framerate=5/1'  ! nv_omx_h264enc quality-level=2 ! mp4mux ! filesink location=/dev/stdout \
   | ffmpeg -y -i - -codec copy   -f flv test.flv</p>
  
  <p>...
  [aac @ 0xebc4c0] Could not find codec parameters for stream 0 (Audio: aac (Main), 7.1, fltp, 1351 kb/s): unspecified sample rate
  Consider increasing the value for the 'analyzeduration' and 'probesize' options
  pipe:: could not find codec parameters
  Input #0, aac, from 'pipe:':
    Duration: N/A, bitrate: 1351 kb/s
      Stream #0:0: Audio: aac (Main), 7.1, fltp, 1351 kb/s
  [flv @ 0xec9280] sample rate not set
  Output #0, flv, to 'test.flv':
      Stream #0:0: Audio: aac, 7.1, 1351 kb/s
  Stream mapping:
    Stream #0:0 -> #0:0 (copy)
  Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
  ubuntu@tegra-ubuntu:~$</p>
  
  <p>Running the commands separately (replacing /dev/stdout with a file) works fine.</p>
  
  <p>If you got it to work and can share how you did it, that would be great. </p>
  
  <p>Thanks.</p>