Subtitle file handler in Python

#!/usr/bin/python3

import os
import re
import shutil

def findVideoFiles(dirname : str):
    ep_re = re.compile(r"(S[0-9]{2}E[0-9]{2})")

    vidfiles = dict()
    # iterate over files in
    # that directory
    for filename in os.listdir(dirname):
        f = os.path.join(dirname, filename)
        
        # checking if it is a file
        if not os.path.isfile(f):
            continue

        #print(filename)
        episodeMatch = ep_re.search(filename)
        if (episodeMatch == None):
            continue

        episode = episodeMatch.group(1)

        fileWithoutExt = os.path.splitext(filename)[0]
        if filename.endswith(".mp4"):
            vidfiles[episode] = fileWithoutExt
        elif filename.endswith(".mv4"):
            vidfiles[episode] = fileWithoutExt
        elif filename.endswith(".mkv"):
            vidfiles[episode] = fileWithoutExt

    return vidfiles

def findBestSubFile(dirname : str):
    bestFile = ""
    bestSize = 0
    for filename in os.listdir(dirname):
        filepath = os.path.join(dirname, filename)
        fileLower = filename.lower()
        if ("english" in fileLower):
            fsize = os.path.getsize(filepath)
            if (fsize > bestSize):
                bestSize = fsize
                bestFile = filepath

    return bestFile

def findDir(searchdir : str, episode : str):
    ep_re = re.compile(r"(S[0-9]{2}E[0-9]{2})")
    for filename in os.listdir(searchdir):
        f = os.path.join(searchdir, filename)
        if (os.path.isdir(f)):
            episodeMatch = ep_re.search(filename)
            if not (episodeMatch == None):
                if (episodeMatch.group(1) == episode):
                    return f
    return None

# find the video files
vids = findVideoFiles(".")

for idx, (episode, vidfile) in enumerate(vids.items()):
    subtitleDir = findDir("./Subs", episode)
    if not (subtitleDir == None):
        subtitleFile = findBestSubFile(subtitleDir)
        shutil.copyfile(subtitleFile, "{:s}.srt".format(vidfile))
        print("Found {:s} in {:s}".format(episode, subtitleDir))