Second, qlv is video, mp3 is audio, so we need to convert qlv to a common video decoder that can accept it, such as mp4
Third, to convert qlv to mp4 or any other decodable formats, you can use editing software (pr, ed, acoustic video, fnc) to separate the output video and audio. But there is a simpler way to convert audio separately in a transcoder, you can download and use beaver, format factory, or magic shadow transcoder