Sur d’autres sites (11676)

• Can anyone help me with the errors ?

  11 juillet 2017, par joel

  I am a newbie to ffmpeg module. Here is my code to read audio wave files using ffmpeg and pipe.

   import numpy as np
  
   import subprocess as sp
  
   import os
  
   from os.path import join
  
   from multiprocessing import Pool
  
   smpler=44100
  
   files= list()
  
  
  
  
  
   for roots, dirs, filek in os.walk("/home/joel/pymusic/mu2"):
  
      for fi in filek:
  
        files.append(os.path.join("/home/joel/pymusic/mu2",fi))
  
  
  
  
  
  def load(filename,in_typ=np.int16,out_typ=np.float32):
  
     channels=1
  
     form={
  
     np.int16:'s16le'
  
       }
  
     f_s= form[in_typ]
  
     command=[
  
       'ffmpeg',
  
       '-i',filename,
  
       '-f',f_s,
  
       '-acodec', 'pcm_' + f_s,
  
       '-ar', str(smpler),
  
       '-ac',str(channels),'-']
  
     raw=b' '
  
     pi=sp.Popen(command, stdout=sp.PIPE, bufsize=4096)
  
     read_c= smpler*channels*16
  
     while True:
  
      data= pi.stdout.read(read_c )
  
      if data:
  
          raw += data
  
      else:
  
          break
  
     audio= np.fromstring(raw, dtype=np.int16).astype(np.float32)
  
     return audio
  
  def helper(f):
  
        return(load(f))
  
  p= Pool()
  
  array= p.map(helper, files)
  
  p.close()
  
  p.join()

  Where files is a list consisting of 20 audio wave files.
  I’m getting the error as :

  >File "prj2.py", line 42, in <module>
  
  >      array= p.map(helper, files)
  
  >File "/usr/lib/python2.7/multiprocessing/pool.py", line 251, in map
  
  >     return self.map_async(func, iterable, chunksize).get()
  
  >File "/usr/lib/python2.7/multiprocessing/pool.py", line 558, in get
  
  >     raise self._value
  
  >ValueError: string size must be a multiple of element size
  
  </module>

  Can anyone help me out with these errors ?

• Issue opening video file with OpenCV VideoCapture

  6 décembre 2017, par user1938805

  I’ve been reviewing the multitudes of similar questions for this issue, but I’m afraid I just cannot figure out why I cannot open a file in opencv

  I have a file "small.avi", which is a reencoding of "small.mp4" that I got from the internet. I reencoded it with ffmpeg -i small.mp4 small.avi, and I did this because I couldn’t open a mp4 file either and online it recommended trying an avi format first.

  Here is my code (mostly copied from a tutorial, with a few lines to show some relevant info) :

  import cv2
  
  import os
  
  
  
  for _, __, files in os.walk("."):
  
      for file in files:
  
          print file
  
  print ""
  
  
  
  cap = cv2.VideoCapture("small.mp4")
  
  print cap.isOpened()
  
  print cap.open("small.avi")
  
  i = 0
  
  while cap.isOpened() and i < 10:
  
      i += 1
  
      ret, frame = cap.read()
  
      print "read a frame"
  
      gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
  
      cv2.imshow('frame', gray)
  
      if cv2.waitKey(1) & 0xFF == ord('q'):
  
          break
  
  cap.release()
  
  cv2.destroyAllWindows()

  This produces the following output :

  "A:\Program Files\AnacondaPY\Anaconda\python.exe" A:/Documents/Final/VideoProcessor.py
  
  small.avi
  
  small.mp4
  
  VideoProcessor.py
  
  
  
  False
  
  False
  
  
  
  Process finished with exit code 0

  My program does not appear to properly open either file. Following the advice of

  Can not Read or Play a Video in OpenCV+Python using VideoCapture

  and

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

  I found my cv2 version to be 3.0.0, went to

  A :\Downloads\opencv\build\x86\vc12\bin

  and copied the file opencv_ffmpeg300.dll to

  A :\Program Files\AnacondaPY\Anaconda

  Despite this, the code still does not successfully open the video file. I even tried the x64 versions, and tried naming the file opencv_ffmpeg.dll, opencv_ffmpeg300.dll, and opencv_ffmpeg300_64.dll (for the x64 version). Is there anything else I can try to fix this ?

  Thanks for any help

• In ffmpeg, how to search to a keyframe BEFORE a specified time ?

  12 janvier 2018, par siods333333

  Background

  For a video in the mp4 or flv container formats, I need to :

  1. Get its duration.

  2. Get a keyframe at 25% of its duration. If frame at 25% isn’t a keyframe, seek to the first keyframe before that frame.

  3. Seek to audio at 10ms before that keyframe.

  According to the following comment on StackOverflow, av_seek_frame seems to only seek to a keyframe after a specified time.

  Question

  Given that it appears I can only seek after a specified time, how is it possible to get the required keyframe and to seek to the correct part in a mp4 or flv container as specified above ?

  My Ideas

  • My best bet is probably parsing the header (and index, where applicable) manually, and then use the av_seek_frame with the AVSEEK_FLAG_BYTE flag.

  • Or I can just walk the whole file, and just check if AVFrame->key_frame is true or not.

  It would be awesome if the trim filter could support different seek methods, but I guess I have to get correct timestamps by myself, is that correct ?