MP3

MP3 support in Audacity
Audacity can both import audio in MP3 format, and export to MP3 format. Audacity can use the MP3 encoding library in order to export MP3s, but we do not distribute LAME because of patent restrictions. Instead, you need to download LAME separately. Instructions for doing this are here in the Audacity Manual.

ID3 Tags
MP3 files contain "metadata" at the start of the file as. These tags typically contain information such as Track Title, Artist Name, Year and Genre. Some of this information may be visible in the playing window of software and hardware players. The tags can be edited with Audacity's tag editor.

By default, the Metadata Editor will always appear at export time. Enter any metadata you require in the editor, then click (not "Save"). The Export window lets you choose the file name, path and any custom encoding settings (by clicking the button).

To prevent Metadata Editor appearing at export time, click, then the tab, and in the "When exporting tracks..." section, uncheck "Show Metadata Editor prior to export step". The tags can still be viewed or edited at any time prior to export at, and the tags in the editor at export time will still be exported.

When using Export Multiple, Metadata Editor pops up as many times as there are files to export. This gives flexibility to adjust the tags separately for tracks which form compilations with different artists or genres. If all the tracks to be exported have common information except for Track Title and Track Number, you may prefer to set Preferences as above so that Metadata Editor does not appear prior to export. Then make any necessary edits to the common tags at prior to export, and the multiple export will proceed silently with the Track Title and Track Number tags added automatically. The Track Title tag will be the same as the file name chosen in the label or track name, and the Track Number tag will be generated according to the order of the labels or tracks.

Each time an MP3 is imported in to a project window, the tags for that file replace the previous content of the Metadata Editor, so if the last imported MP3 has no tags, Metadata Editor will then have no content. If you want to export tags that a previously imported MP3 had, open to change the tags before export. Alternatively you could use to import each MP3 into separate project windows which would preserve the tags for each file.

ID3v2.3 tags are exported. Note that some players don't yet fully support these tags, and so may not see all the tags. To prevent any tags being exported, uncheck "Show Metadata Editor..." in Preferences, open the Editor and delete any text showing in the "Tag Value" fields. Note that when using Export Multiple, the automatically generated Track Title and Track Number tags will still be produced, unless you show Metadata Editor at export and empty all the fields.

ID3v1 is only supported if you use Audacity's command-line encoder and add the --id3v1-only option. ID3v1 should only be needed for very old software or hardware players.

Limitations
In addition to the degrading of sound quality, MP3 files also have a short silence at the beginning. This is not a bug in Audacity or in Lame but is a limitation of the MP3 format. If this is an important issue (for example when making audio loops) you will need to use a format that does not have this limitation, such as WAV, Flac or Ogg.

Re-encoding to MP3
Every time you export from Audacity as an MP3 (or other lossy audio format), this encoding necessarily degrades some of the original quality of the audio. If you import an MP3 into Audacity, edit it then export it as an MP3, you are thus losing quality twice - once in the original MP3 encoding of the imported audio, then again when you export it from Audacity as MP3. Therefore when you are exporting as MP3, work with the highest quality copy of the audio that you can - preferably a copy in a lossless format such as WAV, AIFF or FLAC. You can always obtain a lossless copy of an audio CD by extracting its audio to a WAV or AIFF file. Never extract the audio from a CD to MP3 if you want to export it from Audacity as an MP3.

If you can't avoid importing an MP3 into Audacity and then re-encoding to MP3, don't believe what you sometimes hear that using the same or higher bit rate as the original file will prevent quality loss. This is incorrect. All you can say is that the higher the bit rate you re-encode to, the less will be the quality loss that results.

If you only want to perform simple edits on your MP3 (cut, copy, paste, join, fade or normalize), you may prefer an application that can edit MP3s directly without having to decompress then re-encode them as Audacity does. Examples:
 * MP3 DirectCut for Windows
 * Audion for Mac OS 8, OS 9 and OS X 10.0 to 10.5 (PPC only)
 * Macsome for OS X (Intel Mac only). It can perform lossless split, trim, cut and volume adjustments on M4A files as well as MP3.
 * Mp3Splt for Windows, Mac and GNU/Linux. It can split MP3, OGG and FLAC files by silence detection or by time point (it accepts an Audacity Label Track.txt file as input). It does not perform volume adjustments. It is a command-line tool but you can download the GTK version if you want an interface.

For more advanced edits such as effects, the audio needs to be decompressed in an editor like Audacity, so you must then accept any perceptible quality loss from re-encoding the MP3.