title: Prevent FFmpeg from closing when a named pipe has been read completely
body: <p>I'm doing a C++ application for a university project that takes a video file (e.g. matroska) and using FFmpeg (embedding commands inside <code>std::system()</code> instructions) apply these steps:</p>
  
  <ul>
  <li><p>Extract chunks of frames (e.g. 10 seconds per chunk) and chunks of .aac audio</p></li>
  <li><p>Apply some filters to frames</p></li>
  <li><p>Encode video chunk and audio chunk with x264 and send it to a listening client using RTSP. This step is achieved using two named pipes, one for video and one for audio.</p></li>
  <li><p>Receive the stream into another process and play it using ffplay (on localhost or lan).</p></li>
  </ul>
  
  <p>I need to divide my stream in chunks because I need eventually to satisfy real-time constraints, so I can't apply filters before to my entire input video file and only then start streaming to client.
  My primary problem here is that once FFmpeg has emptied the two pipes, it close; but other chunks of video and audio have still to be piped and streamed. I need FFmpeg to listen to the pipes waiting for new data.</p>
  
  <p>In bash I achieved this with the following commands.</p>
  
  <p><strong>Start to listen in a prompt for a RTSP stream:</strong></p>
  
  <pre><code>ffplay -rtsp_flags listen rtsp://127.0.0.1@127.0.0.1:8090
  </code></pre>
  
  <p><strong>Create a video named pipe and an audio named pipe:</strong></p>
  
  <pre><code>mkfifo video_pipe
  mkfifo audio_pipe
  </code></pre>
  
  <p><strong>Use this command to prevent FFmpeg to close when video pipe is emptied:</strong></p>
  
  <pre><code>exec 7&lt;&gt;video_pipe
  </code></pre>
  
  <p>(it is sufficient to apply it to the pipe video and neither will the audio pipe give problems)</p>
  
  <p><strong>Activate FFmpeg command</strong></p>
  
  <pre><code>ffmpeg -probesize 2147483647 -re -s 1280x720 -pix_fmt rgb24 -i pipe:0 -vsync 0 -i audio_pipe -r 25 -vcodec libx264 -crf 23 -preset ultrafast -f rtsp -rtsp_transport tcp rtsp://127.0.0.1@127.0.0.1:8090 &lt; video_pipe
  </code></pre>
  
  <p><strong>And then feed the pipes in another prompt:</strong></p>
  
  <pre><code>cat audiochunk.aac &gt; audio_pipe &amp; cat frame*.bmp &gt; video_pipe
  </code></pre>
  
  <p>These commands work well using 3 prompts, then I tried them in C++ embedding commands in <code>std::system()</code> instructions (using different threads); everything works, but once ffmpeg command empty the video pipe (finishing first chunk), it closes.
  <code>exec</code> command seems to be uneffective here.
  How could I prevent FFmpeg from closing?</p>
  
  <p>Two days struggling on that problem, viewing all possible internet solution. I hope I was clear despite a great headache, thanks for your suggestions in advance.</p>
  
  <p><strong>UPDATE:</strong>
  My C++ code is something like this; I putted it in a single function on a single thread, but it doesn't change it's behaviour.
  I'm on Ubuntu 18.04.2</p>
  
  <pre><code>void CameraThread::ffmpegJob()
  {
      std::string strvideo_length, command, timing;
      long video_length, begin_chunk, end_chunk;
      int begin_h, begin_m, begin_s, end_h, end_m, end_s;
  
      command = "ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 " + Configurations::file_name;
      strvideo_length = execCmd(command.c_str());
      strvideo_length.pop_back(); // remove \n character
      video_length = strToPositiveDigit(strvideo_length);
  
      if(video_length == -1)
      {
          std::cout &lt;&lt; "Invalid input file";
          return;
      }
  
      std::system("bash -c \"rm mst-temp/mst_video_pipe\"");
      std::system("bash -c \"rm mst-temp/mst_audio_pipe\"");
      std::system("bash -c \"mkfifo mst-temp/mst_video_pipe\"");
      std::system("bash -c \"mkfifo mst-temp/mst_audio_pipe\"");
      // Keep video pipe opened
      std::system("bash -c \"exec 7&lt;&gt;mst-temp/mst_video_pipe\"");
  
      std::string rtsp_url = "rtsp://" + Configurations::my_own_used_ip + "@" + Configurations::client_ip +
              ":" + std::to_string(Configurations::port + 1);
  
      command = "ffmpeg -probesize 2147483647 -re -s 1280x720 -pix_fmt rgb24 -i pipe:0 "
                "-i mst-temp/mst_audio_pipe -r 25 -vcodec libx264 -crf 23 -preset ultrafast -f rtsp "
                "-rtsp_transport tcp " + rtsp_url + " &lt; mst-temp/mst_video_pipe &amp;"; // Using &amp; to continue without block on command
      std::system(command.c_str());
  
      begin_chunk = -1 * VIDEO_CHUNK;
      end_chunk = 0;
  
      // Extract the complete audio track
      command = "bash -c \"ffmpeg -i " + Configurations::file_name + " -vn mst-temp/audio/complete.aac -y\"";
      std::system(command.c_str());
  
      while(true)
      {
          // Define the actual video chunk (in seconds) to use, if EOF is reached, exit
          begin_chunk += (end_chunk - begin_chunk);
          if(begin_chunk == video_length)
              break;
          if(end_chunk + VIDEO_CHUNK &lt;= video_length)
              end_chunk += VIDEO_CHUNK;
          else
              end_chunk += (video_length - end_chunk);
  
          // Set begin and end H, M, S variables
          begin_h = static_cast&lt;int&gt;(begin_chunk / 3600);
          begin_chunk -= (begin_h * 3600);
          begin_m = static_cast&lt;int&gt;(begin_chunk / 60);
          begin_chunk -= (begin_m * 60);
          begin_s = static_cast&lt;int&gt;(begin_chunk);
          end_h = static_cast&lt;int&gt;(end_chunk / 3600);
          end_chunk -= (end_h * 3600);
          end_m = static_cast&lt;int&gt;(end_chunk / 60);
          end_chunk -= (end_m * 60);
          end_s = static_cast&lt;int&gt;(end_chunk);
  
          // Extract bmp frames and audio from video chunk
          // Extract frames
          timing = " -ss " + std::to_string(begin_h) + ":" + std::to_string(begin_m) +
                  ":" + std::to_string(begin_s) + " -to " + std::to_string(end_h) +
                  ":" + std::to_string(end_m) + ":" + std::to_string(end_s);
          command = "bash -c \"ffmpeg -i " + Configurations::file_name + timing +
                  " -compression_algo raw -pix_fmt rgb24 mst-temp/frames/output%03d.bmp\"";
          std::system(command.c_str());
          // Extract audio
          command = "bash -c \"ffmpeg -i mst-temp/audio/complete.aac" + timing +
                  " -vn mst-temp/audio/audiochunk.aac -y\"";
          std::system(command.c_str());
  
          // Apply elaborations on audio and frames.........................
  
          // Write modified audio and frames to streaming pipes
          command = "bash -c \"cat mst-temp/audio/audiochunk.aac &gt; mst-temp/mst_audio_pipe &amp; "
                    "cat mst-temp/frames/output*.bmp &gt; mst-temp/mst_video_pipe\"";
          std::system(command.c_str());
      }
  }
  </code></pre>