Thank you for doing this, I was going to add the optional deps after redoing them (gpodder/gpodder#1761), but haven't had time to do either.

Would the following also work?

-    python3 -m pip install .'[eyed3]' .'[gui]' .'[html5lib]' .'[mutagen]' .'[coverart]' .'[yt-dlp']
+    python3 -m pip install '.[eyed3,gui,html5lib,mutagen,coverart,yt-dlp]'

Can the venv be used on Windows and Linux? Perhaps prepend "Optional:" to the comment, and if required on mac, append "(required on Mac)"?

Do you know if both pip install steps are required, or if only one the following four steps is? I have never used pip but I think the period in '.[gui]' installs the required deps and the brackets install optional deps. I also assume the "as root/user" is a selection, and you don't actually run both of them. If so, we should probably mention that as well.

    # Select one of the following four steps to install:
    # (not including git, python or gtk3 dependencies)

    # required dependencies (as root, or if in virtual environment)
    python3 -m pip install .
    # required dependencies (as user)
    python3 -m pip install --user .
    # required and optional dependencies (as root, or if in virtual environment)
    python3 -m pip install '.[...]'
    # required and optional dependencies (as user)
    python3 -m pip install --user '.[...]'

Would the following also work?

-    python3 -m pip install .'[eyed3]' .'[gui]' .'[html5lib]' .'[mutagen]' .'[coverart]' .'[yt-dlp']
+    python3 -m pip install '.[eyed3,gui,html5lib,mutagen,coverart,yt-dlp]'

The syntax of pip reading from a .toml file is pretty opaque to me, but this does seem to work, yeah.

Can the venv be used on Windows and Linux? Perhaps prepend "Optional:" to the comment, and if required on mac, append "(required on Mac)"?

I imagine so - I can reword it to be more obvious that it's not a mac-specific thing.

Do you know if both pip install steps are required, or if only one the following four steps is? I have never used pip but I think the period in '.[gui]' installs the required deps and the brackets install optional deps. I also assume the "as root/user" is a selection, and you don't actually run both of them. If so, we should probably mention that as well.

    # Select one of the following four steps to install:
    # (not including git, python or gtk3 dependencies)

    # required dependencies (as root, or if in virtual environment)
    python3 -m pip install .
    # required dependencies (as user)
    python3 -m pip install --user .
    # required and optional dependencies (as root, or if in virtual environment)
    python3 -m pip install '.[...]'
    # required and optional dependencies (as user)
    python3 -m pip install --user '.[...]'

Just tried it, it does seem that you don't need both - I'll try rewording it a bit.

Ok, take a look now - I incorporated the changes and squashed all commits together.

Thanks @dconrad5