[KBA-01339] No sound coming through an Axis unit speaker
This article explains why two-way audio might not work over the internet with Axis units in Security Center.
An Axis unit that has an external microphone and a speaker attached is installed at Location X. Office Y hears sound coming from Location X due to the unit's microphone, but Location X cannot hear people speaking from Office Y through the unit's speaker. Both locations are communicating over the internet.
This issue only occurs when the two locations are using the microphone and speaker through Security Center; two-way audio through the unit's web page works properly. All ports are open.
In the Peripherals tab of the Axis unit in Config Tool, set both the speaker and microphone entities to use a Unicast TCP connection type. Also ensure the microphone is set to use the G.711 Data Type.