Trouble downloading a youtube playlist and converting to mp4 with audio/video

I am having difficulty with a side project I am working on. The goal of the program is to be able to do a few functions with a youtube video or playlist link.

1. download a youtube video and audio and merge them.
2. download a youtube playlist's video and audio and merge them.
3. download a youtube video's audio only.
4. download a youtube playlist's audio only.

My main issues arise with the 2. function, downloading a playlist with video and audio and merging them. The program is able to complete function 1 successfully (download a video and audio and merge to one file), and function 3 successfully (download video and output just audio file) Function 4 hasn't been implemented at all yet.

The program is broken into 2 main files: youtube_downloader.py and main.pyThe errors I receive from output of running function 2 are listed after the code below

main.py

from youtube_downloader import download_playlist,input_links,download_video,convert_to_mp3,convert_to_mp4from moviepy.editor import VideoFileClip, AudioFileClip, concatenate_videoclipsimport osprint("Load Complete\n")print('''What would you like to do?(1) Download a YouTube video and audio(2) Download a YouTube Playlist (video and audio)(3) Download a YouTube Video's audio only(4) Download a Youtube Playlist's audio only(q) Quit''')done = Falsewhile done == False:    #ask user for choice    choice = input("Choice: ")    if choice == "1" or choice == "2":        # Sets Quality Option of video(s)        quality = input("Please choose a quality (low or 0, medium or 1, high or 2, very high or 3):")        #download videos manually        if choice == "1":            links = input_links()            print('Download has been started')            for link in links:                 filename = download_video(link, quality)                convert_to_mp4(filename)                print("Download finished!")        #download a playlist        if choice == "2":            link = input("Enter the link to the playlist: ")            print("Downloading playlist...")            filenames = download_playlist(link, quality)            print("Download finished! Beginning conversion...")            **#################################################################            for file in os.listdir('./Downloaded/'):                convert_to_mp4(filenames)            #################################################################**            print("Conversion finished!")    elif choice == "3":        links = input_links()        for link in links:            print("Downloading...")            filename = download_video(link, 'low')            print("Converting...")            convert_to_mp3(filename)            os.remove(filename)    elif choice == "4":        pass        #TODO: add option 4 code    elif choice == "q" or choice == "Q":        done = True        print("Goodbye")    else:        print("Invalid input!")

youtube_downloader.py

import pytubefrom pytube import YouTube, Playlistfrom pytube.cli import on_progressfrom moviepy.editor import VideoFileClip, AudioFileClipimport os"""Downloads video to a 'Downloaded' folder in the same dir as the program."""def download_video(url, resolution):    itag = choose_resolution(resolution)    video = YouTube(url,on_progress_callback=on_progress)    stream = video.streams.get_by_itag(itag)    try:        os.mkdir('./Downloaded/')    except:        pass    stream.download(output_path='./Downloaded/')    return f'./Downloaded/{stream.default_filename}'def download_videos(urls, resolution):    for url in urls:        download_video(url, resolution)def download_playlist(url, resolution):    playlist = Playlist(url)    download_videos(playlist.video_urls, resolution)def choose_resolution(resolution):    if resolution in ["low", "360", "360p","0"]:        itag = 18    elif resolution in ["medium", "720", "720p", "hd","1"]:        itag = 22    elif resolution in ["high", "1080", "1080p", "fullhd", "full_hd", "full hd","2"]:        itag = 137    elif resolution in ["very high", "2160", "2160p", "4K", "4k","3"]:        itag = 313    else:        itag = 18    return itagdef input_links():    print("Enter the links of the videos (end by entering 'stop' or 0):")    links = []    link = ""    while link != "0" and link.lower() != "stop":        link = input("video_url or \"stop\": ")        links.append(link)    if len(links)==1:        print("No links were inputed")        exit()    links.pop()    return linksdef convert_to_mp3(filename):    clip = VideoFileClip(filename)    clip.audio.write_audiofile(filename[:-3] +"mp3")    clip.close()def convert_to_mp4(filename):    video_clip = VideoFileClip(filename)    audio_clip = AudioFileClip(filename)    final_clip = video_clip.set_audio(audio_clip)    final_clip.write_videofile(filename[:-3] +"mp4")    final_clip.close()

Error output

Traceback (most recent call last):  File "C:\Users\ptcoo\Documents\youtube-downloader-converter\main.py", line 44, in <module>    convert_to_mp4(filenames)  File "C:\Users\ptcoo\Documents\youtube-downloader-converter\youtube_downloader.py", line 69, in convert_to_mp4    video_clip = VideoFileClip(filename)                 ^^^^^^^^^^^^^^^^^^^^^^^  File "C:\Users\ptcoo\AppData\Roaming\Python\Python312\site-packages\moviepy\video\io\VideoFileClip.py", line 88, in __init__    self.reader = FFMPEG_VideoReader(filename, pix_fmt=pix_fmt,                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  File "C:\Users\ptcoo\AppData\Roaming\Python\Python312\site-packages\moviepy\video\io\ffmpeg_reader.py", line 35, in __init__    infos = ffmpeg_parse_infos(filename, print_infos, check_duration,            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  File "C:\Users\ptcoo\AppData\Roaming\Python\Python312\site-packages\moviepy\video\io\ffmpeg_reader.py", line 244, in ffmpeg_parse_infos    is_GIF = filename.endswith('.gif')             ^^^^^^^^^^^^^^^^^AttributeError: 'NoneType' object has no attribute 'endswith'