Go to Settings → Audio Codec. Ensure you are using “AAC” for MP4 or “MP3” for AVI. Also verify the source file has an audio track (use MediaInfo to inspect).
Disclaimer: Ultra Video Converter is a third-party tool. Always scan portable executables with updated antivirus software. The author does not host or distribute copyrighted software. Ultra Video Converter 4.4.1021 -Portable-
Don’t let the name fool you—this isn’t just a converter. The software includes a built-in video editor that allows you to: Go to Settings → Audio Codec