Porteus

For example, this command
mpv "${URL}" --term-status-msg="icy-title: ${metadata/icy-title}" | grep -oP "icy-title: \K.*"

returns these two lines:
icy-title:
Jackie Wilson - Reet Petite

But I want only the second line to be output, so just the title.
How does the mpv command need to be modified?

The AI (chatGPT) suggested:

Mpv supports the use of Lua scripts to customize behavior. One such script could extract and output the song title separately:

Create a file called songtitle.lua with the following content:

lua
local msg = mp.get_property_native("metadata/icy-title")
if msg then
local title = string.match(msg, "icy%-title%: (.*)")
if title then
print(title)
end
end

Start mpv with mpv --script=songtitle.lua "${URL}"

This script directly accesses the "icy-title" metadata and extracts the song title using string.match.

Can the mpv command be modified as desired without using a lua script?

That should be possible.
Does somebody has any idea?

my audio files don't seem to give any of that type of metadata.. but anyway
how about just piping to tail like this: the output without the grep part might shed some light on why the grep isn't doing what you want