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• Piping PCM data from FFMPEG to another process with Python subprocess

  1er mars 2019, par Pete Bleackley

  I am trying to transcribe a podcast. To do so, I am decoding the mp3 stream with FFMPEG, and piping the resulting PCM output to the speech recognition component. My code looks like this.

  mp3=subprocess.Popen(['ffmpeg','-i',audio_url,
  
                                '-f','s16le','-ac','1','-ar','16000','pipe:0'],
  
                                stdout=subprocess.PIPE)
  
  sphinx=subprocess.Popen(['java','-jar','transcriber.jar'],
  
                                  stdin=mp3.stdout,
  
                                  stdout=subprocess.PIPE)

  Where audio_url is the url of the mp3 file.

  When I try to run this, it hangs. It appears that feeding the decoded PCM data through the pipe has deadlocked. What can I do to fix this ? The size of the output data is likely to be too big for subprocess.Popen.communicate to be an option, and explicitly calling mp3.stdout.close() has had no effect.

• Play video with FFmpeg in Mac OS

  8 mai 2018, par Maks Ovcharuk

  Need to play video with FFmpeg programmatically in Xcode. We have command line utility, but don’t have controls and components to play (like AVPlayer in AVFoundation).

  Here code in swift 4 :

      let process = Process()
  
      process.launchPath = Bundle.main.path(forResource: "ffmpeg", ofType: "")
  
      process.arguments = ["-i", Bundle.main.path(forResource: "mov", ofType: "mov")!, "-f", "opengl"]
  
  
  
      let pipe = Pipe()
  
      process.standardOutput = pipe
  
  
  
      process.launch()
  
      process.waitUntilExit()
  
  
  
      let data = pipe.fileHandleForReading.readDataToEndOfFile()
  
      let output = NSString(data: data, encoding: String.Encoding.utf8.rawValue) 

• FFMPEG filter 10 frames per second without running through all frames ?

  15 mars 2017, par Kitsune

  I’m trying to process a video through ffmpeg and only need 10 frames per second regardless of the FPS of the original movie file.
  I run the frames through a pipe then call a function to process the frame.

  So what I want is that it scans only 10 frames a second even if the movie runs at 30. So it would for example end up with every 3rd frames (per sec.)

  I’v tried -vf ’select=not(mod(t\,1/10))’ which does make it so that it sends less calls to my function (which reacts to each frames send to a pipe.)

  But the processing takes just as long as without the filter. Setting the -r FPS after the input I receive errors : "[image2pipe @ 0x7fb3d3008a00] Application provided invalid, non monotonically increasing dts to muxer in stream 0 : 788 >= 788" it also does not change the amount of frames being output.

  FFMPEG Commandline :
  FFMPEG_BIN = "ffmpeg"
  command = [ FFMPEG_BIN,
  ’-threads’, ’0’,
  ’-i’, filename,
  ’-f’, ’image2pipe’,
  ’-pix_fmt’, ’rgb24’,
  ’-vsync’, ’0’,
  ’-vf’, ’scale=320:180’, # ,select=not(mod(t\,10/1))
  ’-an’,
  ’-sn’,
  #’-r’, ’10’,
  ’-vcodec’, ’rawvideo’,
  ’-’
  ]
  pipe = sp.Popen(command, stdout=sp.PIPE, bufsize=10**8)

  I send the frames using : process_frame(pipe.stdout.read(width*height*3))
  So far no matter what I try, -r -vf filters.. It either does not speed up, or I still get the full amount of frames calling my function.