| .KRZ | Kurzweil Education | Pliki audio | Kurzweil K2000 File | Kurzweil K2600 | Kurzweil Education |
| .KSC | Korg | Pliki audio | Korg Trinity/Triton Script File | Awave Studio | FMJ-Software |
| .KSD | KeepSafe Software, Inc. | Pliki audio | KeepSafe File | KeepSafe Private Photo Vault | KeepSafe Software, Inc. |
| .KSF | Pandora Tv | Pliki audio | KMPlayer Skin File | KMPlayer | Pandora Tv |
| .KSM | Pfaff | Pliki audio | Pfaff Embroidery Design File Format | Embroidermodder 2 | Open Source |
| .KSS | FabTrol Systems | Pliki audio | FabTrol MRP Template | FabTrol | FabTrol Systems |
| .KT2 | Native Instruments | Pliki audio | Battery 2 Drum Kit File | Native Instruments Kontakt | Native Instruments |
| .KTP | Cakewalk, Inc. | Pliki audio | Kinetic Project Template | Cakewalk SONAR | Cakewalk, Inc. |
| .L | Johan Bontes | Pliki audio | Game Of Life File | Life32 | Johan Bontes |
| .LA | Open Source | Pliki audio | Lossless Audio File | Nullsoft Winamp | Nullsoft |
| .LA1 | LucasArts Entertainment Company, LLC | Pliki audio | LucasArts Game Data File | The Curse of Monkey Island | LucasArts Entertainment Company, LLC |
| .LAA | LucasArts Entertainment Company, LLC | Pliki audio | LucasArts AdLib Audio File Format | Nullsoft Winamp | Nullsoft |
| .LAM | NetScape | Pliki audio | Netscape Media Player Streaming Audio Metafile | Netscape Navigator | NetScape |
| .LDS | GNU Project | Pliki audio | Binutils LD Linker Script | Microsoft Notepad | Microsoft Corporation |
| .LID | Kodak | Pliki audio | Kodak EasyShare Album File | Kodak EasyShare | Kodak |
| .LMS | Light-O-Rama | Pliki audio | Light-O-Rama Musical Sequence Format | Light-O-Rama | Light-O-Rama |
| .LOF | Open Source | Pliki audio | Audacity File List | Audacity | Open Source |
| .LPCM | Microsoft Corporation | Pliki audio | Movie Maker Audio | Microsoft Windows Live Movie Maker | Microsoft Corporation |
| .LQT | Liquid Audio Inc | Pliki audio | Liquid Audio File | Liquid Player | Liquid Audio Inc |
| .LSO | Apple | Pliki audio | Logic Audio Project | Apple Logic Pro | Apple |
| .LVP | Avaya | Pliki audio | Avaya Voice Player Audio File | Avaya Voice Player | Avaya |
| .LWV | Microsoft Corporation | Pliki audio | Linguistically Enhanced Sound File | Microsoft Agent | Microsoft Corporation |
| .M | MathWorks | Pliki audio | MATLAB Source Code File | Notepad++ | Don Ho |
| .M1A | Open Source | Pliki audio | MPEG-1 Audio File | Microsoft Windows Media Player | Microsoft Corporation |
| .M2 | Unknown Developer | Pliki audio | PC-98 Game Music File | FMPMD2000 | Unknown Developer |
| .M22 | Farallon Computing | Pliki audio | Farallon's MacRecorder Recording File | MacRecorder | Farallon Computing |
| .M3A | BirdCage Software | Pliki audio | Enhanced M3U Playlist | JukeBox Decoder | BirdCage Software |
| .M3U | Nullsoft | Pliki audio | Media Playlist File | Microsoft Windows Media Player | Microsoft Corporation |
| .M3U8 | Various Developers | Pliki audio | UTF-8 M3U Playlist File | Microsoft Windows Media Player | Microsoft Corporation |
| .M3V | Unknown Developer | Pliki audio | DJ Mix Pro Playlist | DJ Mix Pro | Unknown Developer |
| .M4A | Apple | Pliki audio | MPEG-4 Audio File | Microsoft Windows Media Player | Microsoft Corporation |
| .M4B | Apple | Pliki audio | MPEG-4 Audio Book File | Microsoft Windows Media Player | Microsoft Corporation |
| .M4P | Apple | Pliki audio | iTunes Music Store Audio File | Apple iTunes | Apple |
| .M4R | Apple | Pliki audio | iPhone Ringtone File | Apple iTunes | Apple |
| .MA1 | Monarch Innovative Technologies Pvt. Ltd | Pliki audio | Monarch Audio File | Monarch Digimix | Monarch Innovative Technologies Pvt. Ltd |
| .MAP | id Software | Pliki audio | Quake Engine Map File | Valve Hammer Editor | Valve |
| .MBR | GNU Operating System | Pliki audio | Master Boot Record File | GNU GRUB | GNU Operating System |
| .MBU | Sony | Pliki audio | Sony CAV-M1000ES Memory Backup File | Sony CAV-M1000ES | Sony |
| .MDC | IBM | Pliki audio | Multi Dimension Cube File | Cognos software | IBM |
| .MDI | Microsoft Corporation | Pliki audio | Microsoft Document Imaging File | Microsoft Office | Microsoft Corporation |
| .MDL | MathWorks | Pliki audio | MathWorks Simulink Model | Simulink | MathWorks |
| .MDR | Olivier Lapicque | Pliki audio | ModPlug Compressed Module | ModPlug Player | Open Source |
| .MDX | Disc Soft Ltd. | Pliki audio | Extended Media Descriptor File | DAEMON Tools | Disc Soft Ltd. |
| .MED | Rockwell Automation Inc. | Pliki audio | RSView Development Project Archive | Rockwell Automation RSView Studio or RSView ME | Rockwell Automation Inc. |
| .MFB | Ensoniq | Pliki audio | Ensoniq MR 76 Audio Fata | MR-76 | Ensoniq |
| .MFF | Cakewalk, Inc. | Pliki audio | Cakewalk MIDI Format | Cakewalk SONAR | Cakewalk, Inc. |
| .MFK | Keiji Mafuka | Pliki audio | Mafuka Audio File | Mafuka Player and Encoder | Keiji Mafuka |
| .MG1 | Microsoft Corporation | Pliki audio | MusiGenesis Project | Music Genesis | Microsoft Corporation |
| .MG2 | PG Music Inc | Pliki audio | Band-in-a-Box Song File | Band-in-a-Box | PG Music Inc |
| .MGB | Nitro2k01 | Pliki audio | Paragon5 Gameboy Tracker Audio | Paragon5 | Nitro2k01 |
| .MGU | PG Music Inc | Pliki audio | Band-in-a-Box MIDI Song | Band-in-a-Box | PG Music Inc |
| .MID | Open Source | Pliki audio | MIDI Audio File | Microsoft Windows Media Player | Microsoft Corporation |
| .MIDI | Synthesia LLC | Pliki audio | MIDI File | Microsoft Windows Media Player | Microsoft Corporation |
| .MIF | Adobe Systems Incorporated | Pliki audio | FrameMaker Interchange Format File | Adobe FrameMaker | Adobe Systems Incorporated |
| .MINIPSF | Un4seen Developments | Pliki audio | Miniature PlayStation Sound Format File | Nullsoft Winamp | Nullsoft |
| .MINIUSF | Nintendo | Pliki audio | Nintendo 64 Song File | Nullsoft Winamp | Nullsoft |
| .MIX | Microsoft Corporation | Pliki audio | Microsoft Image Exchange File | Microsoft Picture It! | Microsoft Corporation |
| .MIZ | Nullsoft | Pliki audio | Winamp Compressed Midi Audio | Nullsoft Winamp | Nullsoft |
| .MJF | Unknown Developer | Pliki audio | Mjuice MP3 Audio File | Nullsoft Winamp | Nullsoft |
| .MKA | Matroska | Pliki audio | Matroska Audio File | MPlayer | The MPlayer Team |
| .MKF | Interscape | Pliki audio | KaraBox Karaoke Music File | KaraBox | Interscape |
| .MKW | Michael K. Weise | Pliki audio | Compressed Audio File | mkwACT | Michael K. Weise |
| .MLD | FMJ-Software | Pliki audio | I-Melody Format For I-Mode | Awave Studio | FMJ-Software |
| .MLP | Meridian Audio | Pliki audio | Meridian Lossless Packing Audio File | MLP Professional Encoder Software | Meridian Audio |
| .MMF | Microsoft Corporation | Pliki audio | Microsoft Message File | Microsoft Exchange Server | Microsoft Corporation |
| .MMM | Magix Software GmbH | Pliki audio | Music Maker Arrangement File | MAGIX Music Maker | Magix Software GmbH |
| .MMP | MixMeister Technology | Pliki audio | MixMeister Studio Playlist | MixMeister Studio | MixMeister Technology |
| .MO3 | Un4seen Developments | Pliki audio | MO3 Audio File | XMMS | Open Source |
| .MOD | Open Source | Pliki audio | Amiga Music Module File | ModPlug Player | Open Source |
| .MOGG | Unknown Developer | Pliki audio | Multitrack Ogg File | Audacity | Open Source |
| .MP1 | RealNetworks | Pliki audio | MPEG-1 Layer 1 Audio File | Apple iTunes | Apple |
| .MP2 | New World Computing | Pliki audio | Heroes Of Might And Magic II Map File | Heroes of Might & Magic III | Ubisoft |
| .MP3 | Moving Picture Experts Group | Pliki audio | MP3 Audio File | Microsoft Windows Media Player | Microsoft Corporation |
| .MPA | Unknown Developer | Pliki audio | MPEG-2 Audio File | Microsoft Windows Media Player | Microsoft Corporation |
| .MPC | Open Source | Pliki audio | Musepack Compressed Audio File | VLC Media Player | VideoLAN |
| .MPGA | RealNetworks | Pliki audio | MPEG-1 Layer 3 Audio File | Microsoft Windows Media Player | Microsoft Corporation |
| .MPR | Open Source | Pliki audio | Bibexcel Data | BibExcel | Open Source |
| .MPY | RCA | Pliki audio | RCA Lyra MP3 Player File | MusicMatch Jukebox | Yahoo! |
| .MPZ | Benetech | Pliki audio | Miradi Project File | Miradi | Benetech |
| .MP_ | Open Source | Pliki audio | Mobile Phone Sound File | BitPim | Open Source |
| .MRA | Unknown Developer | Pliki audio | VilagRadio Recorded Radio Program | Unknown Software | Unknown Developer |
| .MSA | Unknown Developer | Pliki audio | Magic Shadow Archiver Atari Disk Image | Magic Shadow Archiver | Unknown Developer |
| .MSCZ | Open Source | Pliki audio | MuseScore Compressed Score File | MuseScore | Open Source |
| .MSQ | Davidson & Associates, Inc. | Pliki audio | Multimedia Workshop Audio File | Multimedia Workshop | Davidson & Associates, Inc. |
| .MSV | Sony | Pliki audio | Memory Stick Voice File | Microsoft Windows Media Player | Microsoft Corporation |
| .MT2 | Yannick Delwiche | Pliki audio | MadTracker 2 Module | Awave Studio | FMJ-Software |
| .MT9 | Electronics and Telecommunications Research Institute | Pliki audio | Music 2.0 Song | Unknown Software | Unknown Developer |
| .MTE | Yannick Delwiche | Pliki audio | MadTracker 2 Envelope | MadTracker 2 | Yannick Delwiche |
| .MTF | Motorola | Pliki audio | Motorola Theme File | Motorola MOTOCAST USB | Motorola |
| .MTI | Yannick Delwiche | Pliki audio | MadTracker Instrument | Awave Studio | FMJ-Software |
| .MTK | Nullsoft | Pliki audio | MPU-401 Trakker File | Adlib Tracker II | Adlib Tracker II |
| .MTM | VideoLAN | Pliki audio | MultiTracker Module | VLC Media Player | VideoLAN |
| .MTP | Yannick Delwiche | Pliki audio | MadTracker 2 Pattern | MadTracker 2 | Yannick Delwiche |
| .MTS | Sony | Pliki audio | AVCHD Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .MT_ | Passport Music | Pliki audio | Encore Compressed Audio File | Encore | Passport Music |
| .MUI | Myriad Software | Pliki audio | Myriad User Instrument File | Myriad Harmony Assistant | Myriad Software |
| .MUK | Unknown Developer | Pliki audio | Multak Mini 8162 Encoded Audio Karaoke | Unknown Software | Unknown Developer |
| .MUS | MakeMusic, Inc. | Pliki audio | Finale Notation File | SmartMusic | MakeMusic, Inc. |
| .MUSICXML | Michael Good | Pliki audio | Compressed MusicXML File | MuseScore | Open Source |
| .MUSX | MakeMusic, Inc. | Pliki audio | Finale Notation File | SmartMusic | MakeMusic, Inc. |
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