append a string to a modified line

[Mr_Blue]

hello,
thanks to both of you
would you care to explain the code?

    if line.startswith("#EXTINF"): #this makes the loop target a certain line
        out_text +=  line #i see this increments a variable previously set to ""
        name = line.split(",", 1)[1] #i gather this splits line into some sort of array but i fail to grasp its use. 
#could you point me to somewhere this method is explained?
        out_text += f'\n{name}.mp3\n' #at a loss. what's f?
    else:
        out_text += f"{line}\n"

just for the sake of precision, i think it could be good practice to close a file, i guess that print is just to check the whole thing and can be left along, it gives:

in_text = open("playlist.m3u", "r").read()
 
out_text = ""
 
for line in in_text.splitlines():
    if line.startswith("#EXTINF"):
        out_text +=  line
        name = line.split(",", 1)[1]
        out_text += f'\n{name}.mp3\n'
    else:
        out_text += f"{line}\n"
         
with open("new_playlist.m3u", "w") as f:
    f.write(out_text)
f.close()

is it no so?