Isn't the problem that you don't know the pid to kill?

Just a suggestion - maybe it would be easier to have perl streaming the current mp3 to a fifo, and have mpg123 play that? See the .signature example in perlipc for a working example.

Question two: Is there anyway to convince perl to read/write mp3 files without dying

You were already on the right track :)

Here's an example of what I meant in 199077:

adam@2cb:~$ perl -e 'open F, "nofx - falling in love.mp3"; binmode F; 
+open G, ">bleh"; binmode G; while(<F>) { print G; } '
adam@2cb:~$ ls -la nofx\ -\ falling\ in\ love.mp3 bleh 
-rw-r--r--    1 adam     users     5011330 Sep 20 13:00 bleh
-rw-r--r--    1 adam     users     5011330 Jan 24  2002 nofx\ -\ falli
+ng\ in\ love.mp3
adam@2cb:~$ cksum nofx\ -\ falling\ in\ love.mp3 bleh 
2095826934 5011330 nofx - falling in love.mp3
2095826934 5011330 bleh
[download]

The original/new files end up exactly the same - perl is handling the binary data just fine.

update: added binmode G;. example was only working without it because i'm a linux weenie?