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• Pause a FFmpeg encoding in a Python Popen subprocess on Windows

  5 décembre 2020, par CasualDemon

  I am trying to pause an encode of FFmpeg while it is in a non-shell subprocess (This is important to how it plays into a larger program). This can be done by presssing the "Pause / Break" key on the keyboard by itself, and I am trying to send that to Popen.

  


  The command itself must be cross platform compatible, so I cannot wrap it in any way, but I can send signals or run functions that are platform specific as needed.

  


  I looked at how to send a "Ctrl+Break" to a subprocess via pid or handler and it suggested to send a signal, but that raised a "ValueError : Unsupported signal : 21"

  


  from subprocess import Popen, PIPE
import signal


if __name__ == '__main__':
    command = "ffmpeg.exe -y -i example_video.mkv -map 0:v -c:v libx265 -preset slow -crf 18 output.mkv"
    proc = Popen(command, stdin=PIPE, shell=False)

    try:
        proc.send_signal(signal.SIGBREAK)
    finally:
        proc.wait()


  


  Then attempted to use GenerateConsoleCtrlEvent to create a Ctrl+Break event as described here https://docs.microsoft.com/en-us/windows/console/generateconsolectrlevent

  


  from subprocess import Popen, PIPE
import ctypes


if __name__ == '__main__':
    command = "ffmpeg.exe -y -i example_video.mkv -map 0:v -c:v libx265 -preset slow -crf 18 output.mkv"
    proc = Popen(command, stdin=PIPE, shell=False)

    try:
        ctypes.windll.kernel32.GenerateConsoleCtrlEvent(1, proc.pid)
    finally:
        proc.wait()


  


  I have tried psutil pause feature, but it keeps the CPU load really high even when "paused".

  


  Even though it wouldn't work with the program overall, I have at least tried setting creationflags=CREATE_NEW_PROCESS_GROUP which makes the SIGBREAK not error, but also not pause it. For the Ctrl-Break event will entirely stop the encode instead of pausing it.

  


• c# RTSP audio to FFMPEG to SpeechRecognitionEngine

  18 avril 2016, par MrH40XX

  I’m trying to get an audiostream (from any source file/other stream/...) into the microsoft speech recognition engine.

  So far I’ve got :

  ffmpeg.exe -rtsp_transport tcp -i rtsp ://%_return1%/audio -acodec pcm_u16le -f rtp rtp ://localhost:2222

  Then I have inside my code :

  SpeechRecognitionEngine _engine = new SpeechRecognitionEngine(CultureInfo.CurrentCulture);    
  
  this._engine.SetInputToAudioStream(this._rtpClient.AudioStream, new SpeechAudioFormatInfo(16000, AudioBitsPerSample.Sixteen, AudioChannel.Mono));

  Then I have the events registered :

  this._engine.SpeechRecognized += this.SpeechRegocnized;
  
  
  
  this._engine.SpeechDetected += this.EngineOnSpeechDetected;

  I’m not sure about the codec settings... I’ve tried other codecs but doesn’t work.

• Using OpenCV 2.4.4 with FFmpeg in Windows

  22 décembre 2015, par aardvarkk

  I know there are other questions dealing with FFmpeg usage in OpenCV, but most of them appear to be outdated.

  By opening up the makefiles in CMake, I can verify that I’ve got the WITH_FFMPEG flag on. My output folder for the OpenCV build contains a bin folder, within which are Debug and Release folders, each containing a copy of a .dll file entitled opencv_ffmpeg244.dll. I can step into the source code of OpenCV when I create a VideoWriter and verify that the function pointers to the .dll get filled correctly. That much appears to be working.

  If I use the FOURCC code of CV_FOURCC_PROMPT, the following codecs work properly :

  • Microsoft Video 1
  • Intel IYUV codec
  • Logitech Video (I420)
  • Cinepak Codec by Radius
  • Full Frames (Uncompressed)

  The following codecs do not work properly (ie. produce a 0kb video file) :

  • Microsoft RLE

  If my understanding is correct, using FFMPEG should allow for encoding video using a whole bunch of new codecs (x264, DIVX, XVID, and so on). However, none of these appear in the prompt. Manually setting them by their FOURCC codes using the macro CV_FOURCC(...) also doesn’t work. For instance, using this : CV_FOURCC('X','2','6','4') produces the message :

  Could not find encoder for codec id 28: Encoder not found

  and makes a video file of size 0kb.

  Using this : CV_FOURCC('X','V','I','D') produces no error message, and makes a video file of 6kb that will not play in Windows Media Player or VLC.

  I tried manually downloaded the Xvid codec from Xvid.org. Once that was installed, it appeared under the VFW selection in the prompt, and the encoding worked properly. So it’s close to a solution, but if I try to set the FOURCC code directly, it still fails as above ! I have to pick it from the prompt every time. Isn’t FFmpeg supposed to include a whole bunch of codecs ? If so, why am I manually downloading the codec instead of using the one built into FFmpeg ?

  What am I missing here ? Is there a way to check that FFMPEG is "enabled" ? It seems like the only codecs available in the prompt are VFW codecs, not the FFMPEG ones. The .dll has been built and is sitting in the same folder as the executable, but it appears it’s not being used in any way.

  Lots of related questions here. Hoping to find somebody knowledgeable about the FFmpeg implementation in OpenCV and with some knowledge of how all of these pieces fit together.