I hadn't tried adding any new music on hold since upgrading to 2.5 a couple weeks ago. I just tried and I got:
"sh: mpg123: command not found"
My first instinct was to check to see is mpg123 was installed and accessible directly from any shell prompt. I just typed mpg123 in shell and it brought up the various parameter options for mpg123 which told me everything was normal as far as that.
I fixed it by editing /var/www/html/admin/modules/music/page.music.php:
Original Line 207:
"$mpg123cmd = "mpg123 -w \"".substr(...."
$mpg123cmd = "/usr/local/bin/mpg123 -w \"".substr(..."
As you can see, I just told it the complete path to mpg123 on centos and everything works great now. It doesn't keep the .mp3 format though like it use to in 2.4 which I liked as it saved space versus a wav file but I got 120 gigs to spare; I probably will only add but like 20 more songs.