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• How to use ffmpeg in flask server to convert between audio formats without writing files to disk ?

  14 avril 2020, par Athwulf

  I have successfully managed to use ffmpeg in python to convert the format of some audio files like this :

  



  command = "ffmpeg -i audio.wav -vn -acodec pcm_s16le output.wav"
subprocess.call(command, shell=True)


  



  However I want to do this in memory and avoid saving the input and output files to disk.

  



  I have found the follwing code to do such a thing (Passing python’s file like object to ffmpeg via subprocess) :

  



  command = ['ffmpeg', '-y', '-i', '-', '-f', 'wav', '-']
process = subprocess.Popen(command, stdin=subprocess.PIPE)
wav, errordata = process.communicate(file)


  



  But I am struggeling to use this in my context.

  



  I am receiving the file on a server as part of a multipart/form-data request.

  



  @server.route("/api/getText", methods=["POST"])
def api():
    if "multipart/form-data" not in request.content_type:
        return Response("invalid content type: {}".format(request.content_type))
    # check file format
    file = request.files['file']
    if file:
        print('**found file', file.filename)


  



  Now I have the file as a FileStorage Object (https://tedboy.github.io/flask/generated/generated/werkzeug.FileStorage.html). This object has a stream, which can be accessed by using the read method. So I thought I might be able to use this as input for ffmpeg like so :

  



  f = file.read()
command = ['ffmpeg', '-y', '-i', '-', '-f', 'wav', '-']
process = subprocess.Popen(command, stdin=subprocess.PIPE)
wav, errordata = process.communicate(f)


  



  However this yields the the following error :

  



  AssertionError: Given audio file must be a filename string or a file-like object


  



  I have also tried another approach which I found online, using io.BytesIO, to which I can't find the source anymore :

  



  memfile = io.BytesIO()  # create file-object
memfile.write(file.read())  # write in file-object
memfile.seek(0)  # move to beginning so it will read from beginning


  



  And then trying this again :

  



  command = ['ffmpeg', '-y', '-i', '-', '-f', 'wav', '-']
process = subprocess.Popen(command, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
wav, errordata = process.communicate(memfile)


  



  This gets me the following error :

  



  TypeError: a bytes-like object is required, not '_io.BytesIO'


  



  Does anyone have an idea of how to do this ?

  



  Update

  



  The first error message is actually not a error message thrown by ffmpeg. As v25 pointed out correctly in his answer the first approach also returns a bytes object and is also a valid solution.

  



  The error message got thrown by a library (speech_recognition) when trying to work with the modified file. In the unlikely case of someone coming across the same problem here the solution :

  



  The bytes objected returned by ffmpeg (variable wav) has to be turned into a file-like object as the error message implies. This can easily be done like this :

  



  memfileOutput = io.BytesIO(wav)

  


• OpenCV videocapture() not opening video file from hard disk

  8 janvier 2020, par Rossi Riccardo

  Despite being a lot of threads on the issue of open CV not being able to open videos i still can’t manage to solve it.

  I’m trying to open and extract frames using openCV with spyder (os : windows 10, python 3.7.4). As far as i know (provided the file path is correct) cv2.read returns a 0 if either the codec is unsupported (converted the video to H264 to be sure and also downloaded a test avi used to test out this very issue in an older post ) or if there is a problem with the ffmpeg dependency.

  Since i thought this was the source of the issue i added conda and phyton to the PATH with the SETX command and, after that, ended up copying ffmpeg dll and cv2 folders everywhere since i couldn’t understand well were i was supposed to paste it. Results is that i still can’t make it work and can’t even opt to try to make the frame extractor directly with ffmpeg since even that one gives me an error with a copypasted function from it’s site.

  Here is the code :

  import os 
  
  import ffmpeg
  
  
  
  
  
  def read_frame_as_jpeg(in_filename, frame_num):
  
      out, err = (
  
          ffmpeg
  
          .input(in_filename)
  
          .filter('select', 'gte(n,{})'.format(frame_num))
  
          .output('pipe:', vframes=1, format='image2', vcodec='mjpeg')
  
          .run(capture_stdout=True)
  
      )
  
  
  
  # Read the video from specified path 
  
  #cam = cv2.VideoCapture(r'C:\MY\folder\264H.mp4') 
  
  cam = cv2.VideoCapture(r'C:\Users\name\Downloads\drop.avi') 
  
  fps=60
  
  vid_start=371
  
  vid_end=377
  
  sens=20
  
  out_dir=r"C:\MY\folder"
  
  out_dir=out_dir+'\\'
  
  print(out_dir)
  
  
  
  stri="drop.avi"#even tried putting the fiel in the same directory, no change
  
  read_frame_as_jpeg(stri, 1)
  
  
  
  # frame 
  
  currentframe = 0
  
  
  
  while(True): 
  
  
  
      # reading from frame 
  
      ret,frame = cam.read()
  
  
  
      print(currentframe)
  
      if ret and currentframe>= (fps*vid_start)-sens and currentframe<= (fps*vid_end)+sens: 
  
          # if video is still left continue creating images 
  
          name = out_dir+ str(currentframe) + '.bmp'
  
          print ('Creating...' + name) 
  
  
  
          # writing the extracted images 
  
          cv2.imwrite(name, frame) 
  
  
  
          # increasing counter so that it will 
  
          # show how many frames are created 
  
          currentframe += 1
  
      else: 
  
          break
  
  
  
  # Release all space and windows once done 
  
  cam.release() 
  
  cv2.destroyAllWindows()  

  The ffpeg error that i get is

  [WinError 2] Impossible to find the specified file

  while on the other hand since videocapture returns a 0 it doesn’t even enter the loop so i get just a "0" print

• How to use ffmpeg in flask server to convert audio format without writing files to disk ?

  6 janvier 2020, par Athwulf

  I have successfully managed to use ffmpeg in python to convert the format of some audio files like this :

  command = "ffmpeg -i audio.wav -vn -acodec pcm_s16le output.wav"
  
  subprocess.call(command, shell=True)

  However I want to do this in memory and avoid saving the input and output files to disk.

  I have found the follwing code to do such a thing (Passing python’s file like object to ffmpeg via subprocess) :

  command = ['ffmpeg', '-y', '-i', '-', '-f', 'wav', '-']
  
  process = subprocess.Popen(command, stdin=subprocess.PIPE)
  
  wav, errordata = process.communicate(file)

  But I am struggeling to use this in my context.

  I am receiving the file on a server as part of a multipart/form-data request.

  @server.route("/api/getText", methods=["POST"])
  
  def api():
  
      if "multipart/form-data" not in request.content_type:
  
          return Response("invalid content type: {}".format(request.content_type))
  
      # check file format
  
      file = request.files['file']
  
      if file:
  
          print('**found file', file.filename)

  Now I have the file as a FileStorage Object (https://tedboy.github.io/flask/generated/generated/werkzeug.FileStorage.html). This object has a stream, which can be accessed by using the read method. So I thought I might be able to use this as input for ffmpeg like so :

  f = file.read()
  
  command = ['ffmpeg', '-y', '-i', '-', '-f', 'wav', '-']
  
  process = subprocess.Popen(command, stdin=subprocess.PIPE)
  
  wav, errordata = process.communicate(f)

  However this yields the the following error :

  AssertionError: Given audio file must be a filename string or a file-like object

  I have also tried another approach which I found online, using io.BytesIO, to which I can’t find the source anymore :

  memfile = io.BytesIO()  # create file-object
  
  memfile.write(file.read())  # write in file-object
  
  memfile.seek(0)  # move to beginning so it will read from beginning

  And then trying this again :

  command = ['ffmpeg', '-y', '-i', '-', '-f', 'wav', '-']
  
  process = subprocess.Popen(command, stdin=subprocess.PIPE)
  
  wav, errordata = process.communicate(memfile)

  This gets me the following error :

  TypeError: a bytes-like object is required, not '_io.BytesIO'

  Does anyone have an idea of how to do this ?