By default, the video stream will use the audio input of the encoder.  (Typically, the microphone system).

However, you can easily mute/un-mute the audio, simply by clicking the Mute checkbox.

Note: Some splash screens force the audio to mute, depending on how they were setup.  In these cases, you will not be able to un-mute the audio as long as that splash screen is being displayed.

Related Articles:

1. Selecting an Encoder
2. Webcasting Plus- Starting Video Streaming & Recording
3. Webcasting Plus- Display the Splash Screen
4. Webcasting Plus- Pausing and Resuming Streaming / Recording
5. Creating Video Timestamps