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• Using a pipe character | with child_process spawn

  14 septembre 2016, par GreenGiant

  I’m running nodejs on a raspberry pi and I want to run a child process to spawn a webcam stream.

  Outside of node my command is :

  raspivid -n -mm matrix -w 320 -h 240 -fps 18 -g 100 -t 0 -b 5000000 -o - | ffmpeg -y -f h264 -i - -c:v copy -map 0:0 -f flv -rtmp_buffer 100 -rtmp_live live "rtmp://example.com/big/test"

  With child_process I have to break each argument up

  var args = ["-n", "-mm", "matrix", "-w", "320", "-h", "240", "-fps", "18", "-g", "100", "-t", "0", "-b", "5000000", "-o", "-", "|", "ffmpeg", "-y", "-f", "h264", "-i", "-", "-c:v", "copy", "-map", "0:0", "-f", "flv", "-rtmp_buffer", "100", "-rtmp_live", "live", "rtmp://example.com/big/test"];

  camera.proc = child.spawn('raspivid', args);

  However it chokes on the | character :

  error, exit code 64
Invalid command line option (|)

  How do I use this pipe character as an argument ?

• FFmpeg blocking pipe until done ?

  13 mars 2015, par ZeroTek

  I am currently working on a C++ Program (running on Linux) that should run FFmpeg as external Utility to encode the Audio Streams of a Video File to AC3 using popen() and capture the Output through the Pipe.

  Here is a Sample Code on how I tried to achieve this :

  int bufferSize = 2048;
  
  char buffer[bufferSize];
  
  
  
  FILE *handle = popen("ffmpeg  -i filename.mkv -map 0 -codec:v copy -codec:s copy -codec:a ac3 -f matroska -", "r");
  
  int d = fileno(handle);
  
  
  
  while(read(d, buffer, bufferSize) > 0)
  
  {
  
      // Process Data here
  
  }

  Actually this works, but not as I expected. The following happens here : FFmpeg starts, encodes the whole file and my program keeps hanging on read(). Once FFmpeg is done my program continues and reads the data from the pipe.

  But what I actually wanted was to read the output of FFmpeg while it’s encoding the file. Now I wonder how to make it work that Way ? Is FFmpeg blocking the pipe, does not write anything to it until it’s done or is my code not capable of reading while the pipe is written ? Or is there any argument I need to pass to FFmpeg ?

• Python : mp3 to wave.open(f,'r') through ffmpeg pipe

  7 avril 2015, par user2754098

  I’m trying to decode mp3 to wav using ffmpeg :

  import alsaaudio
  
  import wave
  
  from subprocess import Popen, PIPE
  
  
  
  with open('filename.mp3', 'rb') as infile:
  
      p=Popen(['ffmpeg', '-i', '-', '-f', 'wav', '-'], stdin=infile, stdout=PIPE)
  
      ...

  Next i want redirect data from p.stdout.read() to wave.open(file, r) to use readframes(n) and other methods. But i cannot because ’file’ in wave.open(file,’r’) can be only name of file or an open file pointer.

      ...
  
      file = wave.open(p.stdout.read(),'r')
  
      card='default'
  
      device=alsaaudio.PCM(card=card)
  
      device.setchannels(file.getnchannels())
  
      device.setrate(file.getframerate())
  
      device.setformat(alsaaudio.PCM_FORMAT_S16_LE)
  
      device.setsetperiodsize(320)
  
      data = file.readframes(320)
  
      while data:
  
          device.write(data)
  
          data = file.readframes(320)

  I got :

  TypeError: file() argument 1 must be encoded string without NULL bytes, not str

  So is it possible to handle data from p.stdout.read() by wave.open() ?
  Making temporary .wav file isn’t solution.

  Sorry for my english.
  Thanks.