FreePBX allows two styles of music-on-hold customization—static files and streaming. Static files are audio files (such as WAV or MP3 files) that are uploaded to the FreePBX server and played back when a caller is placed on hold. Streaming audio is used to connect to a live audio feed from a particular source. Typically, this would be an Internet stream (many radio stations broadcast over the Internet), but it could also be a stream from a sound card or some other audio device.
FreePBX separates different groups of music on hold into categories. Different static file categories can contain different sets of files. Each streaming category can only contain one audio stream. Music-on-hold categories can be applied to inbound routes (so that all calls that match the route will hear that category) as well as to queues and ring groups. Categories assigned at the call target level will override the music-on-hold category for that particular target only. Once a call leaves...