The PBX had music on hold streaming practically from day one. The feature was originally introduced for the CS410, the infamous hardware appliance in the old pbxnsip days. The hardware platform was able to convert the audio jack analog input into a u-law RTP stream which we used for music on hold.

The CS410 is history; however the music on hold streaming is still part of the software. Instead of using the hardware, we are now using external software tools. It is even possible to use multiple streams. Especially VLC is a powerful and widely available tool that can convert MP3 files and various stream formats into the simple RTP format. Using VLC, there are numerous sources available for all sorts of music on hold.

The biggest obstacle with using VLC and other media streaming services is that the PBX needed to guess the right format. The RTP header ay contain information about the media type; however we had to learn that the streaming services practically stream always non-standard codec numbers. That is why we have changed our strategy of automatically detecting the format to an explicit setting. Even if the administrator has to try out the various possibilities, it is still better to have control instead of being forced to fiddle with VLC.

The only restriction that we have is that the PBX still needs 8 kHz sampling frequency. Almost all music sources offer a much higher sampling frequency; however telephony is still mostly using 8 kHz. The PBX does not deal with the task of sampling the music down; especially when uneven multiple like 44.1 kHz are used, the task of filtering is better left to external tools that do an excellent job in the format conversion.

The latest doc can be found at https://doc.vodia.com/admin_moh