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