| .M15 | Moving Picture Experts Group | Video Files | MPEG Video File | CyberLink PowerDVD | CyberLink |
| .M1PG | Media 100 | Video Files | iFinish Video Clip | iFinish | Media 100 |
| .M1V | Roxio | Video Files | MPEG-1 Video File | CyberLink PowerDVD | CyberLink |
| .M21 | AXMEDIS Products and Services | Video Files | AXMEDIS MPEG-21 File | Apple QuickTime Player | Apple |
| .M2A | Unknown Developer | Video Files | MPEG-1 Layer 2 Audio File | VLC Media Player | VideoLAN |
| .M2P | Moving Picture Experts Group | Video Files | MPEG-2 Program Stream File | Microsoft Windows Media Player | Microsoft Corporation |
| .M2S | Maxthon | Video Files | Maxthon 2 Browser Skin File | Maxthon Cloud Browser | Maxthon |
| .M2T | Roxio | Video Files | HDV Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .M2TS | Sony | Video Files | Blu-ray BDAV Video File | CyberLink PowerDVD | CyberLink |
| .M2V | Webteh | Video Files | MPEG-2 Packetized Elementary Stream | CyberLink PowerDVD | CyberLink |
| .M4S | Ubisoft | Video Files | Myst IV: Revelation Save Game File | Myst IV: Revelation | Ubisoft |
| .M4U | Open Source | Video Files | MPEG-4 Playlist | CyberLink PowerDVD | CyberLink |
| .M4V | Apple | Video Files | iTunes Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .M75 | Moving Picture Experts Group | Video Files | MPEG Video File | CyberLink PowerDVD | CyberLink |
| .MCV | Visicom Media Inc | Video Files | ManyCam Effect File | ManyCam | Visicom Media Inc |
| .MEP | Movavi | Video Files | Movavi Video Editor Project | Movavi Video Editor | Movavi |
| .META | RealNetworks | Video Files | RealPlayer Metafile | RealPlayer Cloud | RealNetworks |
| .MF2 | Adobe Systems Incorporated | Video Files | Authorware Mediator5 Multimedia File | Adobe Authorware | Adobe Systems Incorporated |
| .MJ | Engelmann Media GmbH | Video Files | MovieJack DVD Ripper File | MovieJack | Engelmann Media GmbH |
| .MJ2 | Open Source | Video Files | Motion JPEG 2000 Video | Adobe Premiere Pro CC | Adobe Systems Incorporated |
| .MJP | LG Electronics | Video Files | MJPEG Video File | Apple QuickTime Player | Apple |
| .MJP2 | Open Source | Video Files | Motion JPEG 2000 Video | Adobe Premiere Pro CC | Adobe Systems Incorporated |
| .MJPEG | Various Developers | Video Files | Motion JPEG Video File | Mozilla Firefox | Mozilla |
| .MJPG | Various Developers | Video Files | Motion JPEG Video File | Mozilla Firefox | Mozilla |
| .MK3D | Matroska | Video Files | Matroska 3D Video File | CyberLink PowerDVD | CyberLink |
| .MKV | Various Developers | Video Files | Matroska Video File | CyberLink PowerDVD | CyberLink |
| .ML20 | Apple | Video Files | Mercury Messenger Video File | VLC Media Player | VideoLAN |
| .MMV | Sony | Video Files | MicroMV Video File | Squared 5 MPEG Streamclip | Open Source |
| .MOB | Microsoft Corporation | Video Files | MOBTV Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .MOD | Open Source | Video Files | Amiga Music Module File | ModPlug Player | Open Source |
| .MODD | Sony | Video Files | Sony Video Analysis File | Sony Picture Motion Browser | Sony |
| .MOFF | Sony | Video Files | Sony Video Data File | Sony Picture Motion Browser | Sony |
| .MOI | Unknown Developer | Video Files | MOI Video File | Capty MPEG Edit EX | Pixela Corporation |
| .MOO | Apple | Video Files | Apple QuickTime Movie Clip File | Apple QuickTime Player | Apple |
| .MOOV | Apple | Video Files | Apple QuickTime Movie | CyberLink PowerDVD | CyberLink |
| .MOV | Apple | Video Files | Apple QuickTime Movie | CyberLink PowerDVD | CyberLink |
| .MOVIE | Apple | Video Files | QuickTime Movie File | Apple QuickTime Player | Apple |
| .MP21 | AXMEDIS Products and Services | Video Files | AXMEDIS MPEG-21 Object | AXMEDIS Editor | AXMEDIS Products and Services |
| .MP2V | Roxio | Video Files | MPEG-2 Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .MP4 | Moving Picture Experts Group | Video Files | MPEG-4 Video File | CyberLink PowerDVD | CyberLink |
| .MP41 | Microsoft Corporation | Video Files | Microsoft MP41 Video Data | VLC Media Player | VideoLAN |
| .MP4V | Moving Picture Experts Group | Video Files | MPEG-4 Video File | CyberLink PowerDVD | CyberLink |
| .MPE | Unknown Developer | Video Files | MPEG Movie | VLC Media Player | VideoLAN |
| .MPEG | Unknown Developer | Video Files | MPEG Movie | VLC Media Player | VideoLAN |
| .MPF | Microsoft Corporation | Video Files | Microsoft Media Package File | Microsoft Clip Organizer | Microsoft Corporation |
| .MPG | Moving Picture Experts Group | Video Files | MPEG Video File | CyberLink PowerDVD | CyberLink |
| .MPG4 | Moving Picture Experts Group | Video Files | MPEG-4 Video File | CyberLink PowerDVD | CyberLink |
| .MPJ | Minitab Inc | Video Files | Minitab Project File | Minitab | Minitab Inc |
| .MPL | Sony | Video Files | AVCHD Playlist File | CyberLink PowerDVD | CyberLink |
| .MPLS | Blu-ray Disc Association | Video Files | Blu-ray Movie Playlist Information Data | CyberLink PowerDVD | CyberLink |
| .MPV | Moving Picture Experts Group | Video Files | MPEG Elementary Stream Video File | CyberLink PowerDVD | CyberLink |
| .MPV2 | Roxio | Video Files | MPEG-2 Video Stream | Microsoft Windows Media Player | Microsoft Corporation |
| .MQV | Sony | Video Files | Sony Movie Format File | MPlayer | The MPlayer Team |
| .MSDVD | Microsoft Corporation | Video Files | Windows DVD Maker Project File | Windows DVD Maker | Microsoft Corporation |
| .MSE | CyberLink | Video Files | MediaShow Slideshow Project File | MediaShow | CyberLink |
| .MSH | Martin Schweiger | Video Files | Orbiter 3D Mesh File | Orbiter | Martin Schweiger |
| .MSWMM | Microsoft Corporation | Video Files | Windows Movie Maker Project | Microsoft Windows Live Movie Maker | Microsoft Corporation |
| .MT2S | Open Source | Video Files | MPEG-2 Transport Stream File | CyberLink PowerDVD | CyberLink |
| .MTS | Sony | Video Files | AVCHD Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .MTV | MyMPX.org | Video Files | MTV Video Format File | ShedWorx Smart Converter | Shedworx |
| .MV | Miva | Video Files | MivaScript File | Miva Merchant Script Compiler | Miva |
| .MVB | RealNetworks | Video Files | Multimedia Viewer Book Source File | RealNetworks RealTimes | RealNetworks |
| .MVC | Collectorz.com | Video Files | Movie Collector Catalog | Movie Collector | Collectorz.com |
| .MVD | Magix Software GmbH | Video Files | Movie Edit Pro Movie File | MAGIX Movie Edit Pro | Magix Software GmbH |
| .MVE | BioWare | Video Files | Infinity Engine Movie File | Baldur's Gate | BioWare |
| .MVF | CodeBaby | Video Files | Production Studio Video File | CodeBaby Production Studio | CodeBaby |
| .MVP | Magix Software GmbH | Video Files | MAGIX Video Project File | MAGIX Video Pro X | Magix Software GmbH |
| .MVY | Magix Software GmbH | Video Files | Video Easy Project File | MAGIX Video easy | Magix Software GmbH |
| .MXF | SMPTE | Video Files | Material Exchange Format File | Adobe Premiere Pro CC | Adobe Systems Incorporated |
| .MXM | Next Limit Technologies | Video Files | Maxwell Material File | Maxwell Render | Next Limit Technologies |
| .MXV | Magix Software GmbH | Video Files | MAGIX Video File | MAGIX Movie Edit Pro | Magix Software GmbH |
| .MYS | Vineyard Technologies | Video Files | Vineyard Captured Video File | Vineyard Technologies PC Viewer | Vineyard Technologies |
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