Sometimes, if the video and audio in your Timeline are from separate files, the duration of the audio may be shorter than the video. Stretching the audio to match the video’s duration is not always a good idea- it slows down the audio.
Select the audio source you want to repeat and click on Tools > Repeat Audio. If you have a video track that is five minutes long and an audio track that is one minute long, choosing the ‘Repeat Audio’ option will copy the audio four times into the Timeline sequentially so that it matches the length of the video.
Repeat Audio affects only the last audio source in the an Audio Track, and extends it to the the end of the last piece of video in the Timeline.
When more the one audio source is present in the Timeline, the Repeat Audio option can be used only for the last audio source.