Downloads an entire youtube playlist (or single videos) in mp3 format, deducing and saving artist, name, remixer, tracknumber... If the song has already been downloaded updates only its metadata.

Only the audio data is downloaded.

Imagine a playlist (id 1234567890abcdefghijklmnopqrstuvwx) whose second video (id 0a1b2c3d4e5) is titled
ArtistName feat. Ft1 | SongName [Rel release](Remixer ft. Ft2 remix). The filename would be ArtistName feat. Ft1 | SongName [Rel release](Remixer ft. Ft2 remix)_0a1b2c3d4e5.mp3 and the song's ID3 metadata would be:

artist: "Remixer (original by ArtistName)"
title: "SongName (remix)"
tracknumber: "1"
album: "1234567890abcdefghijklmnopqrstuvwx"

"tracknumber" is 1 because the video is the second one of the playlist

Choose some videos and playlists to download (for example this video and this playlist) and extract their ids (in this case "z-teFykRk0Y" and "PLR0fgOhCSN8ilC2GWuPkipy8FRNp-m-7C").

Then there are two ways to provide the script with those ids: using a file or using command line arguments (all parameters between [square brackets] are to be considered optional; | means or):

In the directory the script is executed in create a file named song-downloader-ids.txt. In that file you can insert the videos/playlists to be downloaded this way:

OPTIONS
ID [DIRECTORY]
ID [DIRECTORY]
...

"OPTIONS" are some options for the script, such as --delete to delete songs that have been removed from the playlists; learn more about them by running in the terminal python3 FILENAME --help. "ID" represents the playlist or video id/url; "DIRECTORY" is optional, represents the directory in which to save the song(s), and defaults to ./ for videos and ./ID/ for playlists. Save the file and run the script. In this case the file could be:

--delete
z-teFykRk0Y ./my_songs/
PLR0fgOhCSN8ilC2GWuPkipy8FRNp-m-7C

Open a terminal and navigate to the "DIRECTORY" the python script is in (run cd DIRECTORY). Then run python3 FILENAME OPTIONS ARGUMENTS (*) replacing "FILENAME" with the name of the script. "OPTIONS" are some options for the script, such as --delete to delete songs that have been removed from the playlists; learn more about them by running in the terminal python3 FILENAME --help. "ARGUMENTS" is the list of videos/playlists to be downloaded and must be formatted this way:

ID [DIRECTORY] - ID [DIRECTORY] - ... - ID [DIRECTORY]

Here "ID" represents the playlist or video id/url; "DIRECTORY" is optional, represents the directory in which to save the song(s), and defaults to ./ for videos and ./ID/ for playlists. If a path contains spaces, you have to sorround it with ". For example (command line commands):

> cd C:/song-downloader/
> python3 song-downloader.py --delete z-teFykRk0Y ./my_songs/ - PLR0fgOhCSN8ilC2GWuPkipy8FRNp-m-7C

(*) Note that the command used for Python is not always python3: it could be py, python, python3.6 or others too.

After the process finishes the folders my_songs (containing Jim Yosef - Smile [Fairytale]_z-teFykRk0Y.mp3) and PLR0fgOhCSN8ilC2GWuPkipy8FRNp-m-7C (containing the playlist) should be in the directory the script is executed in.

• Requires either Python 3.6+ (older versions have not been tested).
• Install dependencies from requirements.txt using this command: python3 -m pip install -r requirements.txt
  It will install the following pip modules: yt-dlp; mutagen.

• The songs are downloaded at the highest possible quality. yt_dlp.YoutubeDL is set up to download the best format that Youtube provides ("bestaudio/best")
• To check if a song has already been downloaded uses the video id saved at the end of the filename, not its file name.
• Automatically renames files whose corresponding video changed name.
• Video ids and playlist ids are automatically distinguished, but if an id refers both to a playlist and to a video only the playlist is downloaded.
• When downloading more videos with the exact same name only the first one is going to be downloaded, and it's going to be saved using the metadata of the last one.
• Videos from platforms other than Youtube may work, but playlists won't. If two videos/playlists from different platforms are downloaded in the same folder, the id contained in their titles may generate conflicts.
• Control characters and '<>:\"/\|?*' are automatically removed from filenames to prevent any problem with filesystems.