I hope that someone that
uses NFO files will come along with a better answer.
Current implementation (v17) is flawed for artists that collaborate on albums, or for sets of CDs, work to be done to fix it. But let's say your music is simple - all albums are 1 CD, and have a single album artist.
An NFO file can be used to provide additional information about an artist or album, and if "Prefer online information" is enabled it can also override some library data previously derrived from music file tags. The information is also the kind of thing that can be scraped from online sources, listed here
http://kodi.wiki/view/Music_tagging#Data_Kodi_Scrapes in wiki (but not well explained).
For albums the xml tags loaded are: "title", "musicBrainzAlbumID", "artistdesc", genre", "style", "mood", "theme", "compilation", "review", "releasedate", "label", "type", "year", "rating", "userrating", "votes", "thumb" plus albumartist credits (name mbid) and tracks (title, duration, mbid and artists). The tracks just get displayed, they are not connected to the songs that you have in your collection. The ability to scrape album artists can really cock up your library if the scraper mis-identifies the album and you have override tags enabled.
For artists the xml tags loaded are: "name", "musicBrainzArtistID", "sortname", "genre", "style", "mood", "yearsactive", "instruments", "born", "formed", "biography", "died", "disbanded", "thumb", "fanart" plus discography (again no connection to the albums that you own).
As you can see many things that don't come from music file tags, plus a few that do. Some example music NFO files would be useful wouldn't it. Here is an artist one:
artist.NFO
Code:
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<artist>
<name>Vonda Shepard</name>
<musicBrainzArtistID></musicBrainzArtistID>
<sortname>Shepard, Vonda</sortname>
<genre>Pop</genre>
<style>Rock/Pop</style>
<yearsactive>1980s - 2010s</yearsactive>
<born>New York City, USA (1963)</born>
<formed></formed>
<biography>Vonda Shepard (born July 7, 1963) is an American pop/rock singer. She appeared as a regular in the television show Ally McBeal from seasons 1-5 in which she played a resident performer at the bar... ....album.</biography>
<died></died>
<disbanded></disbanded>
<thumb preview="http://www.theaudiodb.com/images/media/artist/thumb/ssxxtr1362967460.jpg/preview">http://www.theaudiodb.com/images/media/artist/thumb/ssxxtr1362967460.jpg</thumb>
<fanart>
<thumb preview="http://assets.fanart.tv/preview/music/31e82ae9-f414-4a68-a0bf-d2719368166d/artistbackground/vonda-shepard-4f4011538d212.jpg">http://assets.fanart.tv/fanart/music/31e82ae9-f414-4a68-a0bf-d2719368166d/artistbackground/vonda-shepard-4f4011538d212.jpg</thumb>
<thumb preview="http://assets.fanart.tv/preview/music/31e82ae9-f414-4a68-a0bf-d2719368166d/artistbackground/vonda-shepard-4f40118deecfb.jpg">http://assets.fanart.tv/fanart/music/31e82ae9-f414-4a68-a0bf-d2719368166d/artistbackground/vonda-shepard-4f40118deecfb.jpg</thumb>
<thumb preview="http://assets.fanart.tv/preview/music/31e82ae9-f414-4a68-a0bf-d2719368166d/artistbackground/shepard-vonda-51c751feef2f6.jpg">http://assets.fanart.tv/fanart/music/31e82ae9-f414-4a68-a0bf-d2719368166d/artistbackground/shepard-vonda-51c751feef2f6.jpg</thumb>
</fanart>
<album>
<title>By 7:30</title>
<year>1999</year>
</album>
<album>
<title>Chinatown</title>
<year>2002</year>
</album>
<album>
<title>The Radical Light</title>
<year>1992</year>
</album>
<album>
<title>It's Good Eve</title>
<year>1996</year>
</album>
<album>
<title>From the Sun</title>
<year>2008</year>
</album>
<album>
<title>Vonda Shepard</title>
<year>1989</year>
</album>
</artist>
album.NFO
Code:
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<album>
<title>Their Greatest Hits: The Record</title>
<musicBrainzAlbumID>6136bbcd-fdcd-47b7-bad9-478571076706</musicBrainzAlbumID>
<artist>Bee Gees</artist>
<genre>Rock & Roll</genre>
<style>Bouncy</style>
<mood></mood>
<theme></theme>
<compilation>true</compilation>
<review>Blah.... </review>
<type>Album, compliation </type>
<releasedate></releasedate>
<label>Polydor</label>
<thumb preview="http://assets.fanart.tv/fanart/music/bf0f7e29-dfe1-416c-b5c6-f9ebc19ea810/albumcover/their-greatest-hits-the-record-disc-1-4e06c11518e20.jpg/preview">http://assets.fanart.tv/fanart/music/bf0f7e29-dfe1-416c-b5c6-f9ebc19ea810/albumcover/their-greatest-hits-the-record-disc-1-4e06c11518e20.jpg</thumb>
<path>nfs://192.168.1.50/media/sde1/home/home/xbmc/Music/Bee Gees/Their Greatest Hits_ The Record/</path>
<rating: max=10>8</rating>
<year>2001</year>
<albumArtistCredits>
<artist>Bee Gees</artist>
<musicBrainzArtistID>bf0f7e29-dfe1-416c-b5c6-f9ebc19ea810</musicBrainzArtistID>
</albumArtistCredits>
<track>
<musicBrainzTrackID></musicBrainzTrackID>
<title>Stayin' Alive</title>
<position>1</position>
<duration>00:00</duration>
</track>
<track>
<musicBrainzTrackID></musicBrainzTrackID>
<title>How Deep Is Your Love</title>
<position>2</position>
<duration>00:00</duration>
</track>
...
<track>
<musicBrainzTrackID></musicBrainzTrackID>
<title>You Should Be Dancing</title>
<position>21</position>
<duration>00:00</duration>
</track>
</album>
During scraping Kodi will apply the contents of an artist or album NFO file that it finds in what it determines to be the folder for that album or artist. This has nothing to do with folder names, but taken from the location of the song files for the album or artist.
How do I create an NFO file for music?
Well a simple text editor will do the job, although there are probably media management tools that will do so too. If you have scraped album or artist info from online sources then exporting your music library (from Settings>Media>Library) to separate files (it asks) will sprinkle NFO files throughout your music folders. Frankly I hate that, but it you can then see what a NFO looks like.
What is it the benefit of doing so?
If you are happy with the "wisdom of crowds" that comes from online scraping, or don't care actually about artist bios, or album reviews etc. and so don't scrape online at all then there is none. On the other hand if you like control of your library, or want to use Kodi without an online connection, or move your library without rescraping online, or want to specify additional artist or album info for things that are not well known and so don't scrape online, or use different values for say artist style or album theme etc. then NFO files are the way to do that.