For adding sound into your movie you can either select an existing wave file or record your own file. Click on 'Select Audio Source' in order to select a source (Microphone, speakers, CD, Midi etc. depending on your sound card) for your audio recording.
Selected or recorded audio file can be mixed with the current sound of the video or appended or overwritten.
Volume of the video sound or audio can be increased or decreased by applying volume rates.
Click on 'Add/Mix Audio Into Movie' button to add the specified or recorded sound file into the selected movie file. Then, you can watch the new movie by clicking on the 'Play New Movie File' button.