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• python 3 using ffmpeg in a subprocess getting stderr decoding error

  4 mai 2024, par jdauthre

  I am running ffmpeg as a subprocess and using the stderr to get various bits of data like the subtitles stream Id's. It works fine for most videos, but one with japanese subtitles results in an error :

  


  'charmap' codec can't decode byte in position xxx : character maps to

  


  Much googling suggests the problem is that the japanese requires unicode, whereas English does not. Solutions offered refer to problems with files, and I cannot find a way of doing the same with the stderr. Relevent Code is below :

  


  command = [ffmpeg,"-y","-i",fileSelected,"-acodec","pcm_s16le",
                  "-vn","-t","3", "-f",            "null","-"]
print(command)   
proc = subprocess.Popen(command,stderr=PIPE,Jstdin=subprocess.PIPE,
                            universal_newlines=True,startupinfo=startupinfo)
  
stream = ""    
for line in proc.stderr:
    try:
        print("line",line)
    except exception as error:
        print("print",error)
        line = line[:-1]
        if "Stream #" in line:
            estream = line.split("#",1)[1]
            estream =estream.split(" (",1)[0]
            print("estream",estream)
            stream = stream + estream +"\n"  #.split("(",1)[0] 
            stream = stream + estream +"\n"


  


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

  3 juillet 2017, 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.

  UPDATE

  Thanks to PM 2Ring for hit about io.BytesIO.

  However resulting code does not work.

  import alsaaudio
  
  import wave
  
  from subprocess import Popen, PIPE
  
  
  
  with open('sometrack.mp3', 'rb') as infile:
  
          p=Popen(['ffmpeg', '-i', '-', '-f','wav', '-'], stdin=infile , stdout=PIPE , stderr=PIPE)
  
          fobj = io.BytesIO(p.stdout.read())
  
  fwave = wave.open(fobj, 'rb')

  Trace :

  File "./script.py", line x, in <module>
  
    fwave = wave.open(fobj, 'rb')
  
  File "/usr/lib/python2.7/wave.py", line x, in open
  
    return Wave_read(f)
  
  File "/usr/lib/python2.7/wave.py", line x, in __init__
  
    self.initfp(f)
  
  File "/usr/lib/python2.7/wave.py", line x, in initfp
  
    raise Error, 'not a WAVE file'
  
  wave.Error: not a WAVE file
  
  </module>

  From /usr/lib/python2.7/wave.py :

  ...
  
  self._file = Chunk(file, bigendian = 0)
  
  if self._file.getname() != 'RIFF':
  
      raise Error, 'file does not start with RIFF id'
  
  if self._file.read(4) != 'WAVE':
  
      raise Error, 'not a WAVE file'
  
  ...

  Checking has been failed due to ’bad’ self._file object.

  Inside /usr/lib/python2.7/chunk.py i have found a source of problem :

  ...
  
  try:
  
      self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
  
  except struct.error:
  
      raise EOFError
  
  ...

  Because struct.unpack(strflag+’L’, file.read(4))[0] returns 0.
  But this function works correct.

  As specified here :

  "5-8 bytes - File size(integer)
  Size of the overall file - 8 bytes, in bytes (32-bit integer). Typically, you’d fill this in after creation."
  That’s why my script doesn’t work. wave.open and other functions cannot handle my file object because self.chunksize = 0. Looks like ffmpeg cannot insert File size when using PIPE.

  SOLUTION

  It’s simple.
  I’ve changed init function of Chunk class :

  After :

  ...
  
  try:
  
      self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
  
  except struct.error:
  
      raise EOFError
  
  ...

  Before :

  ...
  
  try:
  
      self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
  
      currtell = file.tell()
  
      if self.chunksize == 0:
  
          file.seek(0)
  
          file.read(currtell)
  
          self.chunksize = len(file.read())-4
  
          file.seek(0)
  
          file.read(currtell)
  
  except struct.error:
  
      raise EOFError
  
  ...

  Of course editing of original module is bad idia. So I’ve create custom forks for 2 classes Chunk and Wave_read.

  Working but unstable full code you can find here.

  Sorry for my awful english.

  Thanks.

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

  16 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.

  UPDATE

  Thanks to PM 2Ring for hit about io.BytesIO.

  However resulting code does not work.

  import alsaaudio
  
  import wave
  
  from subprocess import Popen, PIPE
  
  
  
  with open('sometrack.mp3', 'rb') as infile:
  
          p=Popen(['ffmpeg', '-i', '-', '-f','wav', '-'], stdin=infile , stdout=PIPE , stderr=PIPE)
  
          fobj = io.BytesIO(p.stdout.read())
  
  fwave = wave.open(fobj, 'rb')

  Trace :

  File "./script.py", line x, in <module>
  
    fwave = wave.open(fobj, 'rb')
  
  File "/usr/lib/python2.7/wave.py", line x, in open
  
    return Wave_read(f)
  
  File "/usr/lib/python2.7/wave.py", line x, in __init__
  
    self.initfp(f)
  
  File "/usr/lib/python2.7/wave.py", line x, in initfp
  
    raise Error, 'not a WAVE file'
  
  wave.Error: not a WAVE file
  
  </module>

  From /usr/lib/python2.7/wave.py :

  ...
  
  self._file = Chunk(file, bigendian = 0)
  
  if self._file.getname() != 'RIFF':
  
      raise Error, 'file does not start with RIFF id'
  
  if self._file.read(4) != 'WAVE':
  
      raise Error, 'not a WAVE file'
  
  ...

  Checking has been failed due to ’bad’ self._file object.

  Inside /usr/lib/python2.7/chunk.py i have found a source of problem :

  ...
  
  try:
  
      self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
  
  except struct.error:
  
      raise EOFError
  
  ...

  Because struct.unpack(strflag+’L’, file.read(4))[0] returns 0.
  But this function works correct.

  As specified here :

  "5-8 bytes - File size(integer)
  Size of the overall file - 8 bytes, in bytes (32-bit integer). Typically, you’d fill this in after creation."
  That’s why my script doesn’t work. wave.open and other functions cannot handle my file object because self.chunksize = 0. Looks like ffmpeg cannot insert File size when using PIPE.

  SOLUTION

  It’s simple.
  I’ve changed init function of Chunk class :

  After :

  ...
  
  try:
  
      self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
  
  except struct.error:
  
      raise EOFError
  
  ...

  Before :

  ...
  
  try:
  
      self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
  
      currtell = file.tell()
  
      if self.chunksize == 0:
  
          file.seek(0)
  
          file.read(currtell)
  
          self.chunksize = len(file.read())-4
  
          file.seek(0)
  
          file.read(currtell)
  
  except struct.error:
  
      raise EOFError
  
  ...

  Of course editing of original module is bad idia. So I’ve create custom forks for 2 classes Chunk and Wave_read.

  Working but unstable full code you can find here.

  Sorry for my awful english.

  Thanks.