PAPlayer

PAPlayer (or PAP for short) stands for Psycho-acoustic Audio Player, and it is XBMC's own in-house developed audio-player. PAP originally began as a pure MP3-player using WinAmp's in_mp3.dll for decoding (around 12th of April 2005), but only a few weeks later evolved into a fully-fledged multi-codec music-player.

Currently Supported Codecs
The .dll files for XBMC for Windows or .so files for XBMC for Linux/Mac must be placed under the [XBMCFOLDER]/system/players/paplayer subfolder for the listed music format to become active. If there is no DLL/SO codec available for PAPlayer for a specific format then XBMC will try to play the fle with DVDPlayer instead (DVDPlayer is based on FFmpeg, so if the codec is supported by libavformat and libavcodec in FFmpeg then the chance is that XBMC will be able to play it if you add the audio extension to AdvancedSettings.xml), however is should be noted here that as DVDPlayer is not designed for pure audio-playback you will loose many unique playback advantages/features that PAPlayer has).
 * AAC aka LC-AAC and also AAC+ aka HE-AAC (needs AACCodec.dll from SVN) Based on faac (see i. below)
 * AC3-CDDA (needs AC3Codec.dll from SVN) Based on liba52
 * AC3-WAV (needs AC3Codec.dll from SVN) Based on liba52
 * AIFF short for Audio Interchange File Format (builtin)
 * ALAC aka Apple Lossless (needs AACCodec.dll from SVN) Based on alac
 * APE aka Monkey's Audio (needs MACDll.dll from SVN) Based on MAC (see ii. below)
 * DTS-CDDA (needs DCACodec.dll from SVN) Based on libdca (see iii. below)
 * DTS-WAV (needs DCACodec.dll from SVN) Based on libdca (see iii. below)
 * CDDA aka Audio CD playback, Red Book standard (builtin) Based on libcdio
 * FLAC aka Free Lossless Audio Codec (needs libFLAC.dll from SVN) Based on LibFlac
 * IT (Impulse Tracker modules] modules) Based on Dumb
 * MOD (Tracker Mod audio-module) Based on Dumb
 * MP2 MPEG-1 Audio Layer2 (needs MADCodec.dll from SVN) Based on libmad
 * MP3 MPEG-1 Audio Layer3 (needs MADCodec.dll from SVN) Based on libmad
 * MPC aka Musepack aka Mpeg+ (needs libmpcdec.dll from SVN) Based on libmpcdec 1.2.2
 * OGG VORBIS (needs vorbisfile.dll from SVN) Based on vorbis
 * S3M (Scream Tracker 3 PC music tracker) Based on Dumb
 * SHN aka 'shorten' (needs libshnplay.dll from SVN) Thanks to Holger Stenger for the dll!
 * WAV or WAVE, short for WAVEform audio format (builtin)
 * WavPack (needs wavpack.dll from SVN) Based on wavpack
 * WMA Windows Media Audio (builtin)
 * XBADPCM XBOX ADPCM game audio (ADPCM.dll) Xbox ADPCM plugin 0.1.2
 * XM (like Triton's Fast Tracker modules) Based on Dumb

Currently supported players
(NOT related to XBOX or PS2 ADPCM)
 * IT short for Impulse Tracker (needs dumb.dll from SVN) Based on D.U.M.B 0.93
 * S3M short for Scream Tracker 3 (needs dumb.dll from SVN) Based on D.U.M.B 0.93
 * MOD short for Amiga Module (needs dumb.dll from SVN) Based on D.U.M.B 0.93
 * XM Fast Tracker 2 (needs dumb.dll from SVN) Based on D.U.M.B 0.93
 * NSF NES Sound Format (needs NoseFart.dll from SVN) Based on Nosefart
 * SPC SPC700 sound file (needs snesapu.dll from SVN) Based on alpha-ii's snes APU
 * GYM Genesis music file (needs gensapu.dll from SVN) Based on gens apu
 * SID Commodore 64 Music (needs libsidplay2.dll from SVN) Based on libsidplay2+resid
 * Adlib OPL2/3 FM Music (needs adplug.dll from SVN) Based on adplug (see iv. below)
 * YM ATARI ST music (needs stsoundlibrary.dll from SVN) Based on st sound
 * ADX/AST/ADP/DSP/YMF/HPS Gamecube ADPCM compressed music (needs cube.dll from SVN) Based on in_cube
 * MIDI music (needs timidity.dll from SVN) Based on Timidity (see v. below)

Currently supported tag-standards

 * APEv1
 * APEv2
 * ID3v2
 * ID3v1
 * ID666
 * Vorbis Comments (used by Ogg & Flac)

Other PAP features worth mentioning

 * SSRC resampling from 44.1kHz to 48kHz
 * Gapless support (means if audio is ripped in a certain way, it will playback without gaps)
 * Crossfade tracks (adjustable 1–10 seconds)
 * ReplayGain support
 * Cue sheet support (.cue files) for any supported codec.
 * OGG/OGA chapter support

Supported network-protocols and file-system formats

 * smb:// (Samba)
 * xbms:// (CCX)
 * cdda:// (AudioCD)
 * iso9660://
 * udf://
 * lastfm:// (Last.FM Radio)
 * shout:// (Shoutcast)
 * Local (Hard-disk)