MP3 and MP4 look like two versions of the same thing - as if MP4 were the newer MP3. They aren't. MP3 is an audio file: a song, a podcast episode, a recording, with sound and nothing else. MP4 is a container: a file that usually holds a video and its soundtrack together, and can also carry subtitles and chapters. You'd use an MP3 for something you listen to and an MP4 for something you watch.
#Where the names come from
Both come from MPEG, the standards committee behind most digital video and audio formats, but from different generations. MP3 is short for MPEG-1 Audio Layer III, the sound format from the MPEG-1 standard of 1993, which took over music sharing in the late 1990s. MP4 is the file format defined in part 14 of the much later MPEG-4 family, published in 2003. The "3" and the "4" aren't version numbers of one format - MP3 isn't "MPEG-3", and MP4 isn't an upgraded MP3. MPEG-4 vs MP4 untangles the naming further.
What each file actually is
- Sound only
- Plays on everything, including car stereos and old music players
- A 4-minute song: about 4-10 MB
- Best for music, podcasts, recordings
- Usually video and sound together, plus subtitles or chapters
- Sound inside is usually AAC, not MP3
- A minute of 1080p phone video: about 60 MB
- Best for anything you watch
#Can an MP4 be audio only?
Yes. An MP4 can hold just a soundtrack, and audio-only MP4 files usually use the .m4a extension so apps know there's no picture. iPhone voice memos, songs bought from iTunes, and audio exported from QuickTime are all M4A files. M4A vs MP3 compares the two audio formats directly.
#Is MP4 better than MP3?
For video, there's no contest: MP3 can't hold video at all. For audio, the sound inside an MP4 or M4A is usually AAC, which squeezes a little more quality out of each kilobit than MP3 does, especially at low bitrates. At 192 kbps and above, though, both are indistinguishable from the original for nearly everyone. The real difference is compatibility: MP3 plays on more devices than anything else, which is why it's still the safe choice for music and podcasts.
#Which should you use?
- Music for any device, including cars and older players: MP3.
- Podcasts: MP3 is still the most common format for publishing episodes; Apple Podcasts also accepts M4A.
- Anything with a picture: MP4, with H.264 video and AAC audio for the widest playback.
- Audiobooks: MP3, or M4B (an MP4 audio file with chapters and bookmarks) for Apple Books.
#Converting MP4 to MP3
Turning an MP4 into an MP3 keeps the sound and drops the picture - useful for lectures, interviews, recorded talks or your own performances. Wave's MP4 to MP3 does it in your browser without uploading the file, writing a 192 kbps MP3 that sounds the same as the original on normal speakers and headphones. How to extract audio from a video covers the built-in routes on Mac, Windows and iPhone too.
#Converting MP3 to MP4
Going the other way needs something to show on screen, because an MP4 for YouTube or social media has to have a picture. A video editor can pair the song with a still image or artwork. With ffmpeg it's one command: ffmpeg -loop 1 -i cover.jpg -i song.mp3 -c:v libx264 -tune stillimage -c:a aac -b:a 192k -pix_fmt yuv420p -shortest song.mp4. Wave converts video to MP4 and MP3, but doesn't build videos from audio.
#Does converting lose quality?
MP4 to MP3 re-encodes the sound once. At 192 kbps that loss isn't audible on normal listening gear. What doesn't work is converting a low-quality file to a higher bitrate - a 128 kbps MP3 turned into a 320 kbps MP3 is just a bigger file with the same sound. MP3 bitrate explained covers which bitrate to pick.
#The short version
- MP3 is an audio file. MP4 is a container that usually holds video and sound.
- The names come from different MPEG standards; MP4 isn't a newer MP3.
- Use MP3 for things you listen to, MP4 for things you watch.
- MP4 to MP3 keeps the sound and drops the picture; MP3 to MP4 needs an image to show.