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• Difference between single and double quotes in subprocess [Python 3.4]

  11 décembre 2016, par Vasilis

  I’m using Python 3.4 in Windows Server 12 and I have some Python code that executes the ffmpeg command bellow :

  ffmpeg -i input.mp4 -vf select='not(mod(n\,30)),setpts=N/((30)*TB)' -c:v rawvideo  -pix_fmt uyvy422 -y output.avi

  I use the following code to execute the external command :

  try:
  
      output = subprocess.check_output(command, stderr=subprocess.STDOUT, shell=True)
  
  except subprocess.CalledProcessError as exc:
  
      print ("Command %s failed with error code" % command, exc.returncode, exc.output, file=sys.stderr)

  When I pass the command enclosed in single quotes it successfully runs the command :

  command = 'ffmpeg -i input.mp4 -vf select="not(mod(n\,30)),setpts=N/((30)*TB)" -c:v rawvideo  -pix_fmt uyvy422 -y output.avi'

  When I pass the command as a string enclosed in double quotes it fails :

  command = "ffmpeg -i input.mp4 -vf select='not(mod(n\,30)),setpts=N/((30)*TB)' -c:v rawvideo  -pix_fmt uyvy422 -y output.avi"

  The error message is the following :

  [Eval @ 0000000eaf2fe040] Invalid chars ',setpts=N/((30)*TB)' at the end of expression 'not(mod(n,30)),setpts=N/((30)*TB)'  
  
  [Parsed_select_0 @ 0000000eb0d27ca0] Error while parsing expression 'not(mod
  
  (n,30)),setpts=N/((30)*TB)'  
  
  [AVFilterGraph @ 0000000eb0d0a5a0] Error initializing filter 'select' with args 'not(mod(n\\,30)),setpts=N/((30)*TB)'  
  
  Error opening filters!"

  So it appears that when using double quotes the slash / that is part of the setpts=N/((30)*TB) option is not interpreted correctly, while with double quotes there’s no problem. Note that both commands (either with double or single quotes in the select option) work fine when I run them directly from the command prompt.
  However, I’ve seen many people saying that from a technical perspective single and double quotes make no difference, e.g.

  • http://programmers.stackexchange.com/questions/155176/single-quotes-vs-double-quotes
  • http://programmers.stackexchange.com/questions/155176/single-quotes-vs-double-quotes

  Does slash parsing depend on the quotes around the string or this is just a behavior specific to the executable I’m running ?

• getruntime() exec() with double quotes in command

  29 décembre 2012, par brux

  I want to execute an ffmpeg command, the method I am using works with every command on my list except the following one which contains double quotes to set a filter (-vf) parameter

  ffmpeg -i 2012-12-27.mp4 -vf "movie=bb.png [movie]; [in] [movie] overlay=0:0 [out]" -vcodec libx264 -acodec copy out.mp4

  I have tried changing the quotes for single quotes with no luck. The command works at the android terminal with both single and double quotes.

  The app I'm developing uses about 5 ffmpeg commands, all work except this one, is this some bug ?

  I can't find a concrete solution to this problem, breaking the args into an array and then passing this to runtime().exec() as suggested elsewhere doesn't seem to work, or simply trying to escape the quotes with \" won't work.

  Both of the files referenced in the above command are located in the sdcard, I removed the concatenation of the command out so that things don't get messy, rest assured these commands work in a terminal when referencing the full paths to the files.
  I contatenate the string passed to getRuntime().exec() using a stringbuilder and`getexternalstorageDirectory().getabsolutepath() to get the path to each file like I have been doing with previous commands when using the process class.

  I am using Jelly Bean 4.2 in case that is of any significance.

• Evolution #3257 (En cours) : Permettre de surcharger facilement le nombre d’items affiché dans les...

  30 mars 2021, par cedric -

  c’est dans la PR https://git.spip.net/spip/spip/pulls/146