Using Python to execute a command on every file in a folder

Question

Hello everyone, I'm trying to create a Python script that would :

1. Look into the folder "/input"
2. For each video in that folder, run a mencoder command (to transcode them to something playable on my phone)
3. Once mencoder has finished his run, delete the original video.

That doesn't seem too hard, but I suck at python :)

Any ideas on what the script should look like ?

Bonus question : Should I use

os.system

or

subprocess.call

?

Subprocess.call seems to allow for a more readable script, since I can write the command like this :

cmdLine = ['mencoder', sourceVideo, '-ovc', 'copy', '-oac', 'copy', '-ss', '00:02:54', '-endpos', '00:00:54', '-o', destinationVideo]

EDIT : Ok, that works :

import os, subprocess

bitrate = '100'
mencoder = 'C:\\Program Files\\_utilitaires\\MPlayer-1.0rc2\\mencoder.exe'
inputdir = 'C:\\Documents and Settings\\Administrator\\Desktop\\input'
outputdir = 'C:\\Documents and Settings\\Administrator\\Desktop\\output'

for fichier in os.listdir(inputdir):
 print 'fichier :' + fichier
 sourceVideo = inputdir + '\\' + fichier
 destinationVideo = outputdir + '\\' + fichier[:-4] + ".mp4"

 commande = [mencoder,
      '-of',
      'lavf',
      [...]
      '-mc',
      '0',

      sourceVideo,
      '-o',
      destinationVideo]

 subprocess.call(commande)

os.remove(sourceVideo)
raw_input('Press Enter to exit')

I've removed the mencoder command, for clarity and because I'm still working on it.

Thanks to everyone for your input.

Answer 1

To find all the filenames use os.listdir().

Then you loop over the filenames. Like so:

import os
for filename in os.listdir('dirname'):
     callthecommandhere(blablahbla, filename, foo)

If you prefer subprocess, use subprocess. :-)

Answer 2

Use os.walk to iterate recursively over directory content:

import os

root_dir = '.'

for directory, subdirectories, files in os.walk(root_dir):
    for file in files:
        print os.path.join(directory, file)

No real difference between os.system and subprocess.call here - unless you have to deal with strangely named files (filenames including spaces, quotation marks and so on). If this is the case, subprocess.call is definitely better, because you don't need to do any shell-quoting on file names. os.system is better when you need to accept any valid shell command, e.g. received from user in the configuration file.

Answer 3

AVI to MPG (pick your extensions):

files = os.listdir('/input')
for sourceVideo in files:
    if sourceVideo[-4:] != ".avi"
        continue
    destinationVideo = sourceVideo[:-4] + ".mpg"
    cmdLine = ['mencoder', sourceVideo, '-ovc', 'copy', '-oac', 'copy', '-ss',
        '00:02:54', '-endpos', '00:00:54', '-o', destinationVideo]
    output1 = Popen(cmdLine, stdout=PIPE).communicate()[0]
    print output1
    output2 = Popen(['del', sourceVideo], stdout=PIPE).communicate()[0]
    print output2

Answer 4

Or you could use the os.path.walk function, which does more work for you than just os.walk:

A stupid example:

def walk_func(blah_args, dirname,names):
    print ' '.join(('In ',dirname,', called with ',blah_args))
    for name in names:
     print 'Walked on ' + name

if __name__ == '__main__':
    import os.path
    directory = './'
    arguments = '[args go here]'
    os.path.walk(directory,walk_func,arguments)

Answer 5

Python might be overkill for this.

for file in *; do mencoder -some options $file; rm -f $file ; done

Answer 6

Hi,

I had a similar problem, with a lot of help from the web and this post I made a small application, my target is VCD and SVCD and I don't delete the source but I reckon it will be fairly easy to adapt to your own needs.

It can convert 1 video and cut it or can convert all videos in a folder, rename them and put them in a subfolder /VCD

I also add a small interface, hope someone else find it useful!

I put the code and file in here btw: http://tequilaphp.wordpress.com/2010/08/27/learning-python-making-a-svcd-gui/