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MP3
What is an MP3 file?
The audio format everything plays. Lossy, small, thirty years old and still unbeaten on compatibility.
What MP3 is
MP3 is a codec: the encoding itself rather than the box it travels in. It is used for handing a finished file over, phones and streaming.
The extension is .mp3, and the full name is MPEG Audio Layer III. Both matter less than what the file can hold, which is what the rest of this page is about.
Where MP3 came from
Fraunhofer IIS published it in 1993. The specification is ISO/IEC 11172-3.
A format that has been readable for that long is a format worth trusting with something you want back in ten years.
The specification is public
Anyone can implement it without asking permission or paying a licence, which is why it turns up in so many programs and why files written twenty years ago still open.
Detail is traded for size
MP3 discards detail to stay small, and what it discards does not come back. That is the right trade for something being looked at and the wrong one for something being edited: each re-save takes another bite.
Colour it can describe
Up to 16 bits per channel.
More than eight bits per channel is what stops a gradient from stepping when it is edited, which is why it matters in a working file and rarely in a finished one.
What else it can carry
MP3 can hold a layout that lets it start playing before it has finished arriving.
That matters mostly when converting: whatever the target cannot hold is dropped, usually without a warning.
How many audio channels
Up to 2. Two covers stereo and is what almost everything is; more than two is surround, and it is the part most likely to be folded down when converting to a format that does not define it.
What opens MP3
Audacity, VLC and iTunes read it, and so do most programs of the same kind.
If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.
Opening it in a browser
Every current browser reads it.
That makes it a safe thing to put on a page or attach to a message without wondering what the other end has installed.
What it can carry besides the content
MP3 can hold ID3 tags.
Whether any of it survives a conversion depends entirely on the target, and the honest answer is usually "some of it".
It is a delivery format
MP3 is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.
What goes wrong with it
The recurring complaints: it degrades a little every time it is re-saved.
None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.
The facts, in one place
| Extension | .mp3 |
|---|---|
| Media type | audio/mpeg |
| Published by | Fraunhofer IIS |
| First published | 1993 |
| Specification | ISO/IEC 11172-3 |