You can use Beaver Video Converter, a very easy-to-use format converter that can convert MV to MP3 format, and the sound quality is also very good.

Baidu Search: Beaver All-purpose Video Converter

Step 1: Run the software and add the MV file to the format converter;

Step 2 : Then you can select the audio file you want to convert, and then select the MP3 audio format you want to convert;

Step 3: Then you can set the mp3 music format. Then click Convert in the lower right corner.