| jss | JACOSub Subtitle File |
| jtv | JRiver Recorded TV |
| jvt | JRiver Media Center Recorded Video |
| k3g | Mobile Video |
| kmv | Sansui Mobile DJ Video |
| kux | Youku KUX Video |
| l3 | L3 Media File |
| lmv | LiveSwif Movie |
| lrv | GoPro Low Resolution Video |
| lsf | Streaming Media Format Video |
| lsx | Streaming Media Shortcut |
| ltv | Altitude Express Video |
| lza | Lempel-Ziv-Oberhumer Compressed Animation |
| m00 | Magic Lantern RAW Video |
| m01 | Magic Lantern RAW Video |
| m02 | Magic Lantern RAW Video |
| m03 | Magic Lantern RAW Video |
| m04 | Magic Lantern RAW Video |
| m05 | Magic Lantern RAW Video |
| m1pg | Media 100 iFinish Video Clip |
| m1v | Mpeg Video |
| m2p | Mpeg-2 Program Stream |
| m2ps | Mpeg-2 Program Stream |
| m2t | Transport Stream |
| m2t | Sony AVCHD Video |
| m2ts | Sony AVCHD Video |
| m2v | Mpeg Video |
| m4f | Sony Network Camera MPEG-4 Video |
| m4u | M4U Playlist File |
| m4v | iTunes M4V Video |
| m65 | REI Camera System Video |
| map | HD DVD Advanced Content Time Map |
| mbr | Zune Smooth Streaming File |
| mcam | MediaCam Video |
| mcc | MacCaption Closed Caption File |