Good software for batch audio file conversion.

What's wrong with ffmpeg?

dbPoweramp

Do something like find . -name "*.m4a" -print0 | parallel -0 ffmpeg -i "{}" -c:a libmp3lame -q:a 0 "{.}.mp3"

Another vote for ffmpeg. I wrote a bash script that is basically just a wrapper around a for loop that uses ffmpeg. It asks your input and output type, converts all specified files in the directory, and asks if you want to delete the input files, now I just use that. It ain't much but it's honest work (and the good parts were taken from stackoverflow.)

Foobar2000 is pretty good too for batch converstion.

Just remember that whenever you convert, you are losing fidelity. The only exception is when you convert between lossless formats.

I suggest you get as much music as possible in FLAC, then make mp3 copies you use only for devices that require it. Upgrade equipment when finances allow.

For everything else, also keep your original, like m4a, to keep sound quality at the best you can.

If you're on Linux and need a GUI, SoundKonverter does a good job.

LAME

That's how the program is called. It's a recursive acronym. Lame Ain't an MP3 Encoder (even though that's exactly what it is)

If you don't mind CLI, beets is good at managing this.

I've done that with VLC

MediaHuman YouTube to MP3 has been by far the best one I've found. It does what you're asking

I'm using FFmpeg Batch AV converter for converting several files at once. Its simple and free.

I went thru several ones untill I found the one I use now which does exactly that but I can't remember its name. I'll try to remember check when I get home. The logo had a microphone made to look like a skull if I remember correctly

Edit: MediaHuman youtube to mp3

Also realized that I misunderstood the question

Upgrade your car stereo