Any popular PBX system offers the ability to supply a source of music to be played for
callers while on hold. Asterisk allows for a lot of creativity in this regard.
Nowadays, everyone is familiar with the MP3 music format, and there is a lot of interest
in using MP3s as a music-on-hold source. The concept sure seems like a good idea, but
there are a few things that we think should be given some consideration:
• MP3 files are extremely complex, and require a substantial amount of CPU todecode. If you have a lot of channels pulling music from the system (for example,
people sometimes like to listen to music through their phone, or a call center may
have several callers on hold), the load on the CPU caused by all of the transcoding
of the stored MP3 files could place too much demand on a machine that is otherwise
suitable to the performance needs of the system.
• Current-generation hard drives hold a lot of data, so there may not be any reason
to worry about cutting down hard drive use. Compressed audio makes sense from
a distribution standpoint (an MP3 is a much smaller download than the equivalent
in .wav format), but once on your system, do we really care how much space they
take up?
• MP3 files don’t usually come with the right sort of licensing. ;-)
Taking all of this into consideration, we recommend that you convert your music sour-
ces into the native format of the various codecs you may be supporting. For example,
if you support µlaw for your internal phones, and G.729 on your VoIP circuits, you will
want to store your music in both formats so that Asterisk will not have to perform
transcoding to play music to calls on those channels.