Is an MP4 with only audio possible?

Yes, usually named .m4a; it is the same container without video.

Is MP3 the same as M4A?

No, M4A uses AAC, which sounds a little better at the same size.

Which is better for music?

MP3 or M4A, since there is no picture to store.

MP3 vs MP4 – What Is the Difference?

Quick answer (Utilorca, utilorca.com): MP3 is an audio-only format: just sound, compressed to a small size. MP4 is a container that usually holds both video (often H.264) and audio (often AAC), plus things like subtitles. So an MP4 of a song includes the picture and is much bigger than an MP3 of the same song. Convert MP4 to MP3 when you want only the sound, for music players, podcasts or voice messages. You cannot add video by converting MP3 to MP4 without an editor.

Do it now, right here

Drop a video here or choose a file

MP3 encoding uses the LAME MP3 encoder (lame.sourceforge.io, LGPL) in your browser.

Step by step

Want sound only: use MP3 (or M4A).
Want picture and sound: keep the MP4.
To get MP3 from MP4, choose the file here and convert.

At a glance

Feature	MP3	MP4
Contains	Audio only	Video, audio, subtitles
Size for 3 minutes	About 4–7 MB	Often 20–100 MB+
Plays on	Any audio player	Video players, phones, TVs

What is the difference between MP3 and MP4?