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• Prevent FFmpeg from closing when a named pipe has been read completely

  21 octobre 2019, par Werther Berselli

  I’m doing a C++ application for a university project that takes a video file (e.g. matroska) and using FFmpeg (embedding commands inside std::system() instructions) apply these steps :

  • Extract chunks of frames (e.g. 10 seconds per chunk) and chunks of .aac audio

  • Apply some filters to frames

  • 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.

  • Receive the stream into another process and play it using ffplay (on localhost or lan).

  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.

  In bash I achieved this with the following commands.

  Start to listen in a prompt for a RTSP stream :

  ffplay -rtsp_flags listen rtsp://127.0.0.1@127.0.0.1:8090

  Create a video named pipe and an audio named pipe :

  mkfifo video_pipe
  
  mkfifo audio_pipe

  Use this command to prevent FFmpeg to close when video pipe is emptied :

  exec 7<>video_pipe

  (it is sufficient to apply it to the pipe video and neither will the audio pipe give problems)

  Activate FFmpeg command

  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 < video_pipe

  And then feed the pipes in another prompt :

  cat audiochunk.aac > audio_pipe & cat frame*.bmp > video_pipe

  These commands work well using 3 prompts, then I tried them in C++ embedding commands in std::system() instructions (using different threads) ; everything works, but once ffmpeg command empty the video pipe (finishing first chunk), it closes.
  exec command seems to be uneffective here.
  How could I prevent FFmpeg from closing ?

  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.

  UPDATE :
  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

  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 << "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<>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 + " < mst-temp/mst_video_pipe &"; // Using & 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 <= 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<int>(begin_chunk / 3600);
  
          begin_chunk -= (begin_h * 3600);
  
          begin_m = static_cast<int>(begin_chunk / 60);
  
          begin_chunk -= (begin_m * 60);
  
          begin_s = static_cast<int>(begin_chunk);
  
          end_h = static_cast<int>(end_chunk / 3600);
  
          end_chunk -= (end_h * 3600);
  
          end_m = static_cast<int>(end_chunk / 60);
  
          end_chunk -= (end_m * 60);
  
          end_s = static_cast<int>(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 > mst-temp/mst_audio_pipe &amp; "
  
                    "cat mst-temp/frames/output*.bmp > mst-temp/mst_video_pipe\"";
  
          std::system(command.c_str());
  
      }
  
  }
  
  </int></int></int></int></int></int>

• How do I get duration of an In Memory Video in Python / Django ?

  19 juillet, par Lucas Tonon

  So I was successfully using the following code to get the duration of a saved video in Django.

  



  def get_video_length(file_path):
command = [
    'ffprobe',
    '-v',
    'error',
    '-show_entries',
    'format=duration',
    '-of',
    'default=noprint_wrappers=1:nokey=1',
    file_path
  ]

try:
    output = check_output( command, stderr=STDOUT ).decode()
except CalledProcessError as e:
    output = e.output.decode()

return output


  



  But now I need to get the duration of an uploaded file before saving it.
I have a serializer with a FileField and on validate method I should check the video duration.
For instance :

  



  class VideoSerializer(serializers.Serializer):
video = serializers.FileField(required=True, validators=[validate_media_extension, validate_video_duration])


  



  Then on validate_video_duration I needed to call some method like get_video_length, but I need an alternative to get the duration from the video in memory. The object that I have is an instance of InMemoryUploadedFile (https://docs.djangoproject.com/en/2.2/_modules/django/core/files/uploadedfile/)

  


• Vcpkg building FFmpeg with libxml2

  15 décembre 2019, par Subestima

  First off all im a newbie in this area so if im asking something really stupid or non sense im sorry in advance, so lets get right to the point... im trying to add features to the ffmpeg, and by what i know i have to modify CONTROL file and portfile.cmake but as it seems its not enough i dont understand the errors and i cant get more info about this in the internet so if you could give me some info how to do it properly it would allready mean a lot to me ! i will leave the portions of code and error file

  **portfile.cmake:**
  
  if("libxml2" IN_LIST FEATURES)
  
      set(OPTIONS "${OPTIONS} --enable-libxml2")
  
  endif()
  
  
  
  **CONTROL:**
  
  Feature: libxml2
  
  Description: Libxml2 is the XML C parser and toolkit developed for the Gnome project (but usable outside of the Gnome platform)
  
  Build-Depends: zlib, libiconv, liblzma
  
  
  
  **Command Prompt after (vcpkg install ffmpeg[libxml2]:x64-windows)**
  
  CMake Error at scripts/cmake/vcpkg_execute_required_process.cmake:72 (message):
  
      Command failed: C:/vcpkg/downloads/tools/msys2/msys64/usr/bin/bash.exe --noprofile --norc C:/vcpkg/ports/ffmpeg\build.sh C:/vcpkg/buildtrees/ffmpeg/x64-windows-rel C:/vcpkg/buildtrees/ffmpeg/src/n4.2-02d8c63f80 C:/vcpkg/packages/ffmpeg_x64-windows "--enable-asm --enable-yasm --disable-doc --enable-debug --enable-runtime-cpudetect --enable-libxml2 --disable-openssl --disable-ffmpeg --disable-ffplay --disable-ffprobe --disable-libvpx --disable-libx264 --disable-opencl --disable-lzma --disable-bzlib --enable-avresample  --disable-static --enable-shared --extra-cflags=-DHAVE_UNISTD_H=0  --extra-cflags=-MD --extra-cxxflags=-MD"
  
      Working Directory: C:/vcpkg/buildtrees/ffmpeg/x64-windows-rel
  
      Error code: 1
  
      See logs for more information:
  
        C:\vcpkg\buildtrees\ffmpeg\build-x64-windows-rel-out.log
  
  
  
  Call Stack (most recent call first):
  
    ports/ffmpeg/portfile.cmake:197 (vcpkg_execute_required_process)
  
    scripts/ports.cmake:94 (include)
  
  
  
  
  
  Error: Building package ffmpeg:x64-windows failed with: BUILD_FAILED
  
  Please ensure you're using the latest portfiles with `.\vcpkg update`, then
  
  submit an issue at https://github.com/Microsoft/vcpkg/issues including:
  
    Package: ffmpeg:x64-windows
  
    Vcpkg version: 2019.09.12-nohash**strong text**
  
  
  
  **Log Error file:**
  
  === CONFIGURING === ERROR: libxml-2.0 not found using pkg-config
  
  
  
  If you think configure made a mistake, make sure you are using the latest version from Git.  If the latest version fails, report the problem to the ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.freenode.net. Include the log file "ffbuild/config.log" produced by configure as this will help solve the problem.

  Thank you for your attention,
  Regards Pedro Cunha !