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• Python subprocess : capture output of ffmpeg and run regular expression against it

  31 décembre 2014, par Jesse Adam

  I have the following code

  import subprocess
  
  import re
  
  from itertools import *
  
  
  
  command = ['ffprobe', '-i', '/media/some_file.mp4']
  
  p = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  
  text = p.stderr.read()
  
  retcode = p.wait()
  
  text = text.decode('utf-8')
  
  p = re.compile("Duration(.*)")
  
  
  
  num = 0 #for debugging
  
  for line in iter(text.splitlines()):
  
      print(str(num) + line) #for debugging
  
      m = p.match(str(line))
  
      if m != None:
  
          print(m.group(1))

  When I look at the output there is a line that says "Duration" on it, however it is not captured, print(m.group(1)) is never reached. If I change the text variable to a hardcoded string of "Duration blahblah" I get " blahblah", which is what I expect. It seems like the regex doesn’t recognize the text coming back from stderr. How can I get the text into a format that the regex will recognize and match on ?

  ---

  I have come up with the following solution, should it help anyone else attempting to capture duration from ffmpeg using python

  import subprocess
  
  import re
  
  
  
  command = ['ffprobe', '-i', '/media/some_file.mp4']
  
  p = subprocess.Popen(command, stderr=subprocess.PIPE)
  
  text = p.stderr.read()
  
  retcode = p.wait()
  
  text = text.decode('utf-8')
  
  p = re.compile(".*Duration:\s([0-9:\.]*),", re.MULTILINE|re.DOTALL)
  
  m = p.match(text)
  
  print(m.group(1))

• Extract individual macroblock types and their corresponding motion vectors [closed]

  14 mai 2023, par Prajit Kumar

  I need to make a pair for each macroblock from a frame of a video containing its type and motion vector.

  


  I extracted motion vectors by using the python module of mv-extractor.

  


  For macroblock type I used ffmpeg command : ffmpeg -threads 1 -debug 'mb_type' -i file.h264 -f null -

  


  The info received from ffmpeg command doesn't match with the location of motion vectors extracted (Macroblocks which are divided into smaller blocks of size 8X16 or 16X8 do not match with the info of macroblock size received in motion vector info). Also, the ffmpeg command for extracting macroblock type doesn't work properly on some videos.

  


  Can you please tell a more streamlined way of doing this task.

  


• Different ffmpeg result after saving to png

  28 juillet 2023, par Kalev Maricq

  Saving images to PNG first seems to produce different ffmpeg encodes. Running this test code

  


  from PIL import Image
import cv2
import ffmpeg
import hashlib

ffmpeg.input('test.jpg').output('testff.png').run()
cv2.imwrite('testcv.png',cv2.imread('test.jpg'))
Image.open('test.jpg').save('testpil.png')

hashes=[]
for suf in ['.jpg','ff.png','cv.png','pil.png']:
    dest='test'+suf.replace('.','')+'.mp4'
    ffmpeg.input('test'+suf).output(dest).run()
    hashes.append(hashlib.file_digest(open(dest,'rb'),'md5').hexdigest())
    
print(hashes)


  


  I get
  
['a5b744a8ac0f6de9ec4de43ff737c46e'
  
,'ab62474f2160899e064ba24890047372'
  
,'baa788d5e4ef212ab610b8b5cf7772cb'
  
,'baa788d5e4ef212ab610b8b5cf7772cb']

  


  As you can see, the only two that match are the cv2 and pillow conversions, and none of them match the original. In terms of file size, the results that passed to png first seem to be about 10% smaller than the direct-from-jpg result.

  


  Why is this happening and how can I avoid changing image data until I'm ready to encode ?