Q:

Python 2.7 mediainfo --inform outputs full info rather than one string

Using the following in powershell produces the expected output of 01:22:02:03:
 MediaInfo --Language=raw --Full --Inform="Video;%Duration/String4%" filename

My following python 2.7 script always gives the full mediainfo output with every piece of metadata, not just the Duration String that I specified.. I've tried escaping the semi colons but it has no effect.  What am I doing wrong? 
import sys
import subprocess
filename = sys.argv[1]
test = subprocess.check_output(['MediaInfo', '--Language=raw', '--Full', '--inform="Video;%Duration/String4%"', filename])
print test

A:

Lose the double-quotes in the --Inform argument.  I can reproduce your problem with this code:
import subprocess

args =  [
    'mediainfo',
    '--Language=raw',
    '--Full',
    '--inform="Video;%Duration/String4%"',
    'tests/reference.mp4'
]

bad_output = subprocess.check_output(args)
line_count_bad = len(bad_output.splitlines())

args[3] = args[3].replace('"', '')

good_output = subprocess.check_output(args)
line_count_good = len(good_output.splitlines())

print(line_count_bad, line_count_good, sep='\t')
print(good_output)

The output is:
204 1
b'00:00:07:08\n'

