Python gist to obtain video details like duration, resolution, bitrate, video codec and audio codec, frequency using 'ffmpeg'

getVideoDetails.py

#! /usr/bin/env python                                                                                                                                                             
import os
import sys
import re
import tempfile

def getVideoDetails(filepath):
    tmpf = tempfile.NamedTemporaryFile()
    os.system("ffmpeg -i \"%s\" 2> %s" % (filepath, tmpf.name))
    lines = tmpf.readlines()
    tmpf.close()
    metadata = {}
    for l in lines:
        l = l.strip()
        if l.startswith('Duration'):
            metadata['duration'] = re.search('Duration: (.*?),', l).group(0).split(':',1)[1].strip(' ,')
            metadata['bitrate'] = re.search("bitrate: (\d+ kb/s)", l).group(0).split(':')[1].strip()
        if l.startswith('Stream #0:0'):
            metadata['video'] = {}
            metadata['video']['codec'], metadata['video']['profile'] = \
                [e.strip(' ,()') for e in re.search('Video: (.*? \(.*?\)),? ', l).group(0).split(':')[1].split('(')]
            metadata['video']['resolution'] = re.search('([1-9]\d+x\d+)', l).group(1)
            metadata['video']['bitrate'] = re.search('(\d+ kb/s)', l).group(1)
            metadata['video']['fps'] = re.search('(\d+ fps)', l).group(1)
        if l.startswith('Stream #0:1'):
            metadata['audio'] = {}
            metadata['audio']['codec'] = re.search('Audio: (.*?) ', l).group(1)
            metadata['audio']['frequency'] = re.search(', (.*? Hz),', l).group(1)
            metadata['audio']['bitrate'] = re.search(', (\d+ kb/s)', l).group(1)
    return metadata

if __name__ == '__main__':
    if len(sys.argv) != 2:
        print("Usage: ./getVideoDetails.py <filepath(absolute or relative)>")
        sys.exit("Syntax Error")
    print( getVideoDetails(sys.argv[1]) )

Few video files i tried all i get is {}
Is it supposed to be specific video formats?