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• Error issuing complex shell command in python via subprocess

  4 juillet 2018, par user16171

  I’ve converted about 100 video tapes and now have 100 folders full of .dv files (each folder’s name is a date). In each folder, I want to combine all of the .dv files into one x265 mp4. I have figured out the ffmpeg command to do this, and I’ve written a simple Python script to traverse the folder hierarchy and print out the ffmpeg command to do each folder’s conversion. I’d like to set it up to just run each folder in series - it will take about a week to do the entire conversion, leaving me with about 5GB of video to use/post, etc. vs the 1.5TB of raw .dv files.

  The shell command looks like this :

  ffmpeg -f concat -i <(for f in FULL_PATH_TO_FILES/*.dv; do echo "file '$f'"; done) \
  
    -c:v libx265 -crf 28 -c:a aac -b:a 128k \ 
  
    -strict -2 FULL_PATH_TO_FILES/FOLDERNAME.mp4

  I can run that as a shell command, and it works fine. I could use the python script to generate the 100 commands and just copy and paste them into my shell one at a time. But I’d rather just have them run in series.

  I’ve tried various incarnations of os.system and subprocess.call or subprocess.Popen, and they all error.

  I build up the command and issue subprocess.call(command), which gives this error :

  "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 522, in call
  return Popen(*popenargs, **kwargs).wait()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 710, in init
  errread, errwrite)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 1335, in _execute_child
  raise child_exception
  OSError : [Errno 2] No such file or directory

  I’ve also tried building up the command, as described in many of the other threads I’ve read, but it does not work, and I assume it’s because of the for-loop I have in the shell command.

  So, what’s the best way to do this ? Obviously, a shell-jockey could just tell me how to do this via the shell, but I’m more comfortable using Python to traverse the directories and build up the ffmpeg command.

  For what it’s worth, here is the whole script :

  import os
  
  import subprocess
  
  t1 = "ffmpeg -f concat -i <(for f in "
  
  t2 = "/*.dv; do echo \"file '$f'\"; done) -c:v libx265 -crf 28 -c:a aac -b:a 128k -strict -2 "
  
  t3 = ".mp4"
  
  rootDir = ROOTDIR
  
  for dirName, subdirList, fileList in os.walk(rootDir):
  
      S = dirName.split('/')    
  
      if S[-1] == "Media":
  
          moviename = S[-2].split(".")[0] # e.g. "19991128_Thanksgiving"
  
          command = t1 + dirName + t2 + dirName + "/" + moviename + t3
  
          if sum([".mp4" in fname for fname in fileList]) == 0: # don't bother if there is already a mp4 file in the folder
  
              cmd_list = [t1,dirName,t2,dirName,"/",moviename,t3]
  
              print command
  
              print
  
              print
  
              subprocess.call(command)

• Convert PNGs to webm video with transparency

  2 juillet 2018, par sebastian

  I would like to use avconv to convert a series of PNG images to a WebM video, preserving transparency.

  I understand that the pixel format used in the output video must support transparency. So I tried :

  $ avconv -framerate 25 -f image2 -i frames/%03d.png -pix_fmt yuva420p output.webm

  Unfortunately, avconv complains :

  Incompatible pixel format 'yuva420p' for codec 'libvpx-vp9', auto-selecting format 'yuv420p'

  I am using ffmpeg version 2.8.4-1+b1 Copyright (c) 2000-2015 the FFmpeg developers.

• Convert PNGs to webm video with transparency

  20 septembre 2016, par sebastian

  I would like to use avconv to convert a series of PNG images to a WebM video, preserving transparency.

  I understand that the pixel format used in the output video must support transparency. So I tried :

  $ avconv -framerate 25 -f image2 -i frames/%03d.png -pix_fmt yuva420p output.webm

  Unfortunately, avconv complains :

  Incompatible pixel format 'yuva420p' for codec 'libvpx-vp9', auto-selecting format 'yuv420p'

  I am using ffmpeg version 2.8.4-1+b1 Copyright (c) 2000-2015 the FFmpeg developers.