1. Introduction

Aqualung is an advanced music player originally targeted at the GNU/Linux operating system, today also running on FreeBSD, OpenBSD and Microsoft Windows. It plays audio CDs, internet radio streams and podcasts as well as soundfiles in just about any audio format and has the feature of inserting no gaps between adjacent tracks. It also supports high quality sample rate conversion between the file and the output device, when necessary.

Audio CDs can be played back and ripped with on-the-fly conversion to WAV, FLAC, Ogg Vorbis or CBR/VBR MP3 (gapless via LAME). Seamless tagging of the created files is offered as part of the process. Internet radio stations streaming Ogg Vorbis or MP3 are supported. Subscribing to RSS and Atom audio podcasts is supported: Aqualung can automatically download and add new files to the Music Store. Optional limits for the age, size and number of downloaded files can be set.

Almost all sample-based, uncompressed formats (e.g. WAV, AIFF, AU etc.), as well as files encoded with FLAC (the Free Lossless Audio Codec), Ogg Vorbis, Ogg Speex, MPEG Audio (including the infamous MP3 format), MOD audio formats (MOD, S3M, XM, IT, etc.), Musepack and Monkey's Audio Codec are supported. Numerous formats and codecs are also supported via the FFmpeg project, including AC3, AAC, WMA, WavPack and the soundtrack of many video formats. There is also a native (non-FFmpeg) WavPack decoder. The program can play the music through OSS, ALSA, sndio, PulseAudio, the JACK Audio Connection Kit, or even using the Win32 Sound API (available only under Cygwin or native Win32). Depending on the compile-time options, not all file formats and output drivers may be usable in a particular build. Type aqualung -v to get a list of all the compiled-in features.

Aqualung supports the LADSPA 1.1 plugin standard. You can use any suitable plugin to enhance the music you are listening to.

Other features of the program are: tabbed playlist, internally working volume and balance controls (not touching the soundcard mixer), multiple skin support, random seeking during playback, track repeat, list repeat and shuffle mode (besides normal playback). In track repeat mode the looping range is adjustable. Aqualung will come up in the same state as it was when you closed it, including playback modes, volume and balance settings, currently processing LADSPA plugins, window sizes, positions and visibility, and other miscellaneous options. Aqualung has the ability to display and edit Ogg Xiph comments, ID3v1, ID3v2 and APE tags, as well as FLAC picture frames found in files that support them. See the section about metadata support for full reference.

The method of assembling the title string of a track is programmable (via a user-provided Lua function) and can include nearly any metadata item or audio file attribute. See the documentation of the Lua extension file config setting for full reference.

You can control any running instance of the program remotely from the command line (start, stop, pause etc.). Remote loading or enqueueing soundfiles as well as complete playlists is also supported.

In addition to all this, Aqualung provides a so-called Music Store that is an XML-based music database, capable of storing various metadata about music on your computer (including, but not limited to, the names of artists, and the titles of records and tracks). You can (and should) organize your music into trees of Artists/Records/Tracks, thereby making life easier than with the all-in-one Winamp/XMMS playlist. Importing file metadata (ID3v1, ID3v2 tags, Ogg Xiph comments, APE metadata) into the Music Store as well as getting track names from a CDDB/FreeDB database is supported. For audio CDs, CD-Text retrieval is also implemented.