HD encoders normally use the embedded audio alongside the video. However, when the audio is coming from elsewhere you can insert it via the Line-in on the rear of the unit.
To set this up, click the Configure button on the Cards page alongside the video input card you wish to change:
Next, expand the Alt. Audio Source drop down in the Advanced group box and choose System input. If the video and audio paths are out of sync, you may need to adjust them with the Audio processing correction (ms) setting:
You will need to reload for the changes to become active. From a connections standpoint, the following diagram illustrates that you must use the blue 3.5mm jack socket for line in audio.
