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• What does the variable ${i%.*} mean in terminal ?

  17 mars 2020, par wongz

  This shell command converts all .avi to .mp4 as per this answer by @llogan

  Can someone explain how $i%.* works ?
  In particular, what does % do ?

  for i in *.avi; do ffmpeg -i "$i" "${i%.*}.mp4"; done

• Why is `subprocess.call` not invoking the command

  6 juin 2014, par Shookie

  I’m trying to run a .wav file through ffmpeg using the subprocess.call(shell=True) in the following code and it doesn’t seem to run. I know this because the output_file isn’t created and I’m getting an exception in the open() method.
  What am I doing wrong ?

  try:
  
      import pocketsphinx
  
  
  
  except:
  
      import pocketsphinx as ps
  
      import sphinxbase
  
      import subprocess
  
      import os
  
  
  
  hmmd = "../../Pocketsphinx_Files/en-us-8khz"
  
  lmdir = "../../Pocketsphinx_Files/cmusphinx-5.0-en-us.lm"
  
  dictp = "../../Pocketsphinx_Files/cmu07a.dic"
  
  
  
  output_filename = "../../temp/ps_output.wav"
  
  
  
  def recognize(filename="../../temp/temp_output.wav"):
  
  
  
      command = "ffmpeg -i "+filename+" -ac 1 -ab 16 -ar 16000 "+output_filename
  
  
  
      subprocess.call(command,shell=True)
  
  
  
      wavFile = open(output_filename,"rb")
  
  
  
      speechRec = ps.Decoder(hmm = hmmd, lm = lmdir, dict = dictp)
  
  
  
      wavFile.seek(44)
  
  
  
      speechRec.decode_raw(wavFile)
  
  
  
      result = speechRec.get_hyp()
  
  
  
      #os.remove(filename)
  
      #os.remove(output_filename)
  
  
  
      return result
  
  
  
  if __name__=="__main__":
  
      print(recognize())

  edit : I’ve got ffmpeg installed.
  Furthermore, when I run the subprocess.call() command from the python interpreter it seems to work. This is why I’m stumped.

• FFMPEG not working as intended in a bash script

  9 mai 2024, par rcp

  I'm trying to get the mean volume of a recording and the echo the expected value. When I do it line by line, everything works fine, but as soon as I execute it in a bash script, I have a problem with the FFMPEG line. I identified the problem, which is that &> analysis is not doing anything for some reason and instead of saving the output in a file it prints it in the shell.

  


  I don't know how to fix it since it works fine when not in a script.

  


  #!/bin/bash

# Record sound
sh aud2.sh

# Run ff.sh in the background to analyze volume and save results
ffmpeg -i test.wav -af "volumedetect" -vn -sn -dn -f null - &> analysis.vol

# Extract mean_volume and save to mean.vol
grep "mean_volume" analysis.vol > mean.vol

# Extract numerical value and save to val.vol
sed -n 's/^.*mean_volume: \([-0-9.]*\) dB.*/\1/p' < mean.vol > val.vol

# Read the value from val.vol into the variable volume
volume=$(code>

  


  Expected output when line by line

  


  Actual output in bash script

  


  I expected the shell output to be saved in a file.