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• Cannot open ".mp4" video files using OpenCV 2.4.3, Python 2.7 in Windows 7 machine

  24 octobre 2017, par TJ Monserrat

  I am currently working on a project that involves reading mp4 video files.
  The problem I encountered is that it using Python 2.7 (32 bit), OpenCV 2.4.3 (cv2.pyd) in a Windows 7 machine.

  The code snippet is as follows :

  try:
  
          video = cv2.VideoCapture("video.mp4")
  
  except:
  
          print "Could not open video file"
  
          raise
  
  print video.grab()

  "video.grab()" always returns false : meaning it doesn’t read the file "video.mp4"
  But when we try this :

  try:
  
          video = cv2.VideoCapture("video.avi")
  
  except:
  
          print "Could not open video file"
  
          raise
  
  print video.grab()

  "video.grab()" returns true : meaning it is able to read ".avi" files.

  Another is we have tried this same snippet on Linux and Mac and it seems to work fine, meaning it is able to read both mp4 files and avi files.

  This problem is similar to this problem and this problem. Both still don’t have a clear and workable answer.

  I would appreciate any help or workaround aside from just using Linux or Mac for programming this as I need this to work on all three systems.

• 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.

• Cannot open video in OpenCV (Python)

  22 mai 2017, par Abeer Yosef

  I am trying to open video in openCV but it is not working i found solutions by adding full path i.e "D :/Folder1/Folder2/1.avi", converting video to .avi instead of mp4, copy the dll file from open cv to python folder after changing it is name by opencv version and windows 64 bit ffmpeg opencv_ffmpeg320_64.dll
  my opencv version 3.2.0
  windows 64
  python2.7 and Anaconda2

  I am beginner in Python and unfortunately nothing of the above solved my problem.

  below my code snippet :

  import numpy as np
  
  import cv2
  
  
  
  cap = cv2.VideoCapture('1.avi')
  
  if cap.isOpened():
  
      print "opend"
  
  else:
  
      print "not opend"
  
  
  
  while(cap.isOpened()):
  
      ret, frame = cap.read()
  
  
  
      gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
  
  
  
      cv2.imshow('frame',gray)
  
      if cv2.waitKey(1) & 0xFF == ord('q'):
  
          break
  
  
  
  cap.release()
  
  cv2.destroyAllWindows()