Vivox: Why does audio volume shift on iOS when using Vivox?

Note: Similar behavior can seen when using the AVAudioSessionCategoryPlayback  category

When using Vivox on iOS, the AudioSession category must be set to AVAudioSessionCategoryPlayAndRecord before you initialize the Vivox SDK as part of your Obj-C/C++ application code, which is detailed in Why am I not transmitting audio in iOS? For more information, see the Apple developer documentation on AVAudioSessionCategoryPlayback and AVAudioSessionCategoryPlayAndRecord.

It is recommended that you change the AVAudioSession category before standard audio playback of your application. This is because changing the AVAudioSession when audio is playing can cause unexpected audio volume shifts for your users.

Note: This is a side effect of changing the AVAudioSession category during playback and is not caused by Vivox.