Optional parse parameters

[Spenhouet]

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What i want to achieve:

For example, if i want to download all Songs from this youtube channel: EMH Music

There are songs that have the following titles:

1. Joachim Pastor - Laos
2. Erland - Liquid (Chiaro Remix)
3. [Electro House] Blaynoise - Devil's Dance
4. [Dark Electro] Owl Vision - Oblique (Mathematic Remix)

As you can see there ist different metadata in the title, like the artist, track, genre, alt_title.

I would like to read all of this metadata in a single run.

How it works (doesn't work) at the moment:

If i define a parse string like
--metadata-from-title "[%(genre)s] %(artist)s - %(title)s (%(alt_title)s)"
the parsing only works on the Song 4 and fails on 1, 2 and 3.

Possible solutions:

Add a optional flag

There could be a character in the parse string that flags some part as optional.
For example: "?[%(genre)s] ?%(artist)s - %(title)s? (%(alt_title)s)?"
This string would still get the artist and title if the genre or alt_title is missing.

Allow multiple parse strings:

There could me multiple parse strings. If the first fails, the second one is parsed and so on. If it doesn't fail it doesn't parse the other strings.
For example:
--metadata-from-title "[%(genre)s] %(artist)s - %(title)s (%(alt_title)s)"
--metadata-from-title "%(artist)s - %(title)s (%(alt_title)s)"
--metadata-from-title "[%(genre)s] %(artist)s - %(title)s"
--metadata-from-title "%(artist)s - %(title)s"