Quod Libet

Rhythmbox (the music player that comes with Debian) is pretty good. Fine most of the time. But it does have a problem with compilation albums. Investigating the issue before, I'd found that Banshee will play compilation albums correctly, but in the process of installing it on Squeeze I noticed it has an obsolete dependency bug, so I gave it a miss. On a whim I tried Quod Libet again. Lenny came with version 1 which didn't impress me too much, but Squeeze has version 2 which is a big improvement. It recognised my compilation albums correctly- and what's more its excellent tag editor allowed me to fix some tagging errors I hadn't noticed before.
The default GUI is pretty basic, can be customised to show a paned browser, album covers, a search feature, playlists etc. (These features are also available in a separate window.)

The basic GUI:


Album cover view:


The Tag Editor:


The download album art plugin:


Quod Libet comes with many plugins that can be enabled if desired. I really liked the album cover search feature which works really well- no more Google searches and file saving- it's all automatic.
I also used the notify plugin to get new track notifications, and the tray icon plugin to put the music player in the notification area rather than close it completely. (I like to keep the bottom panel for documents and keep my music player separate.) This is probably the weakest feature of the player (although it is only a plugin.) Hovering over the Quod Libet icon only gives track information- not album art and track progress like other players. The panel icon is also indistinct when paused (a bug?)
[Update: not a bug. The plugin superimposes the Gnome paused icon (which depends on the theme selected) over the Quod Libet icon. Unfortunately in a dark panel, the Quod Libet icon does not display well, as it is black with a white border (so only the border shows. Editing the Quod Libet icon to white helps.]
Other plugins worth a look would be the MusicBrainz and CDDB lookup plugins for identifying audio tracks. (I looked previously at other programs using MusicBrianz and CDDB.)
Despite the minor gripe about the tray icon plugin, I'll give Quod Libet five stars for handling compilation albums, having one of the best tag editors around, a brilliant album cover finder and an elegant and customisable GUI. And I haven't looked at all the features yet- for example, Quod Libet claims to be better able to handle large music libraries than other players.

Music file tags

Rip a CD and the ripping program will often go online and look up the album, artist and track information, and append this information to the audio file as a tag. Sound Juicer does this in Ubuntu. But how does it work, and is it possible to automatically tag audio files that have been ripped without tagging? This issue caused me some confusion recently.
I used Audiograbber to rip some CD's into MP3 on a Windows computer. The program didn't prompt me to add the tag information, so I assumed it didn't have this facility (looking at the website now, I see it does). The result was several folders of MP3 files with no meaningful file names or tag information.
I decided to look for a way to automatically tag and name the files. I found EasyTAG. The program gave me an option to search the something called the CDDB database to look up the CD details. For several of my folders of MP3's, this worked. For one folder, the program found the CD in the database, but one track didn't match up. In frustration, I tried MP3Tag in Windows. Using the same CDDB database (freedb.org) and entry, the program correctly tagged the folder. (Ho hum.)
But I was left in some confusion. Apart from not seeing that I could have used Audiograbber to look up the files when I ripped them, I hadn't really understood what how EasyTAG and MP3Tag found the metadata for my files, as this post to the Ubuntu Forum proves.
So how does CDDB work? Wikipedia has a good explanation. The CDDB database uses a "discid" created from track duration information stored in the table-of-contents of the CD.
So how had EasyTAG recognised my already-ripped MP3 files without a table-of-contents? I'd assumed it must have used an "audio fingerprint", but I was obviously wrong. I can only guess that EasyTAG and MP3Tag use track length information to create a discid.
So is there a way to identify audio files using an "acoustic fingerprint"? Yes, MusicBrainz Picard can do it in Linux. (Winamp in Windows uses Gracenote.)