MP4 vs MP3
They are not rivals: MP4 is a video format and MP3 is an audio format. Keep a video as MP4; when all you want is the sound (a song, a podcast, a lecture), convert it to MP3, which is far smaller and plays on everything that plays music.
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Choose MP4 when
- Anything with a picture: a recording, a clip, a film.
- A file you will want to watch again, or edit.
- When the sound has to stay in step with the picture.
Choose MP3 when
- Music, podcasts and audiobooks, where there is nothing to watch.
- Listening on a phone, in a car or on a speaker that only plays audio.
- When the file has to be small: an hour of MP3 at 128 kbps is about 55 MB.
What MP4 actually is
MP4 is a container: it holds a video stream, usually H.264, an audio stream, usually AAC, and any subtitles or chapter data, and describes how they line up. Almost every device made in the last fifteen years plays that combination in hardware, which is why MP4 became the default.
Two MP4 files can behave completely differently depending on the codecs inside. A file that will not play is usually an unusual codec in an ordinary container, not a broken file.
What MP3 actually is
MP3 discards the parts of a sound that psychoacoustic models say you are least likely to hear, then compresses the rest. It was the format that made digital music portable, and while newer codecs beat it at every bitrate, nothing matches its compatibility.
Converting an MP3 to another lossy format compounds the damage, because the second encoder is guessing at audio the first one already threw away.
MP4 and MP3 side by side
| MP4 | MP3 | |
|---|---|---|
| Extension | .mp4 | .mp3 |
| Media type | video/mp4 | audio/mpeg |
| Inside the file | H.264 video with AAC sound | MPEG-1 Layer III |
| Compression | Lossy | Lossy |
| Carries sound | Yes | Yes |
| Plays on | every phone, laptop, TV, browser and messaging app | everything, including car stereos and hardware twenty years old |
| We can write it | Yes | Yes |
Questions
Is MP4 video or audio?
MP4 is a video format. It usually holds video and sound together, but it can hold sound alone, which is what an M4A file is. MP3 only ever holds sound.
Does converting MP4 to MP3 lose quality?
The picture is dropped and the sound is re-encoded. At 192 kbps or more the difference is very hard to hear, unless the sound in the video was low quality to begin with.
Can I turn an MP3 into an MP4?
Only by adding something to look at. An MP4 made from an MP3 is either sound only or needs a still image, which is what video sites ask for.