You can set up a voice-only session when instantiating a Publisher object:
There are a number of user interface optimizations that you can make in a voice-only session:
Getting audio levels — The OpenTok client libraries include events that
report the audio level of a subscriber or publisher. For more information, see these topics:
Speaker detection — You can use the audio level events to detect active speakers in a session.
For an example using OpenTok.js, see this topic.
Displaying a custom volume indicator — You can use the audio level events to display a
volume indicator (such as a meter). For an example using OpenTok.js, see
Setting an image to display in audio-only mode — You can display an image in a
Publisher or Subscriber that is in audio-only mode. In OpenTok.js, see
In iOS and Android, you can simply add an image to the view hierarchy of the app.
In the OpenTok Android SDK, you can have the audio played back using the headset speaker (which is preferable in
a voice-only session). See Setting
the audio output mode for a voice session.
When archiving a voice-only session, you can specify that the archive include audio only
(not video) when you create the archive. See the
archiving developer guide.