You can try Pazera Free Audio Extractor or AoA Audio Extractor Basic. Both are free. Or DVD Audio Extractor if you want more features.
If you reconvert to mp3 you will lose quality depending on the audio bitrate you choose.
You can try using PgcDemux to first demux the VOB, then use BeLight (just drag in the BeSweet files over) to convert the extracted audio to MP3.
The audio in VOB files is most likely AC3. You can demux that, as above, with e.g., PGCdemux, and get exactly the same audio as an AC3 file.
This may be 1, 2, 5 or 6 channels.
Most media players can play AC3 as-is, so you may not need to convert it at all.
If you do want to convert to MP3, that is stereo only, so you may need to downmix it.
There are many audio converters, e.g. Foobar2000.
来源：https://forum.videohelp.com/threads/342684-How-to-extract-audio-from-vob-files