Simple example of using ffmpeg as a Python subproc

Question

I'm looking to convert a large directory of movies from one format to another, and to check in on the status of the conversion. I'm programming in Python.

Something like this:

>> m = MovieGenerator()
>> m.convertMovie('/path/to/movie/movie1.avi')
>> print m.status
>> 35 frames completed

Is this possible (or recommended)? Does anyone have a working example of how to use ffmpeg as a subprocess?

Once the conversion is happening, is there any way to "check in" on the status of the conversion (for example, how many frames have been completed?)

Answer 1

For a large directory of movies, I'd use multiprocessing.Pool, to set up a pool workers. Each then converts files using subprocess. I use the following script to do AVI to MKV conversion in batches:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Author: R.F. Smith <[e-mail]>
#
# To the extent possible under law, Roland Smith has waived all copyright and
# related or neighboring rights to avi2mkv.py. This work is published from the
# Netherlands. See http://creativecommons.org/publicdomain/zero/1.0/

"""Convert all AVI files found in the direcory trees named on the command line
   to Theora/Vorbis streams in a Matroska container."""

import base64
import os
import sys
import subprocess
from multiprocessing import Pool, Lock

globallock = Lock()

def tempname(ext):
    """Create a name for a temporary file in the /tmp firectory.

    Keyword arguments:
    ext -- the extension (without .) to give to the file.
    """
    return '/tmp/' + base64.b64encode(os.urandom(12), '__') + '.' + ext

def findavi(dirlist):
    """Find AVI files and returns their names in a list.

    Keyword arguments:
    dirlist -- a list of directories to seach in
    """
    result = []
    for dirname in dirlist:
        for root, dirs, files in os.walk(dirname):
            for name in files:
                if name.endswith('.avi'):
                    result.append(root + '/' + name)
    return result

def output(txt):
    """Print while holding a global lock."""
    globallock.acquire()
    print txt
    globallock.release()        

def process(fname):
    """Use ffmpeg2theora and mkvmerge to convert an AVI file to Theora/Vorbis
    streams in a Matroska container.

    Keyword arguments:
    fname -- name of the file to convert
    """
    ogv = tempname('ogv')
    args = ['ffmpeg2theora', '--no-oshash', '-o', ogv, '-v', '7', fname]
    args2 = ['mkvmerge', '-o', fname[:-3] + 'mkv', ogv]
    bitbucket = open('/dev/null')
    try:
        output("Converting {} to {}.".format(fname, ogv))
        subprocess.check_call(args, stdout=bitbucket, stderr=bitbucket)
        output("Starting merge for {}.".format(ogv))
        subprocess.check_call(args2, stdout=bitbucket, stderr=bitbucket)
        os.remove(ogv)
        output("Conversion of {} completed.".format(fname))
    except:
        output("ERROR: Converting {} failed.".format(fname))
    bitbucket.close()

def main(argv):
    """Main program.

    Keyword arguments:
    argv -- command line arguments
    """
    if len(argv) == 1:
        path, binary = os.path.split(argv[0])
        print "Usage: {} [directory ...]".format(binary)
        sys.exit(0)
    avis = findavi(argv[1:])
    p = Pool()
    p.map(process, avis)
    p.close()

if __name__ == '__main__':
    main(sys.argv)