| nwc | NoteWorthy Composer Music |
| nwctxt | NoteWorthy Composer Text |
| nwp | NoteWorthy Player Music |
| nw_ | Compressed NoteWorthy Composer Music |
| nxt | NeXTSTEP Sound File |
| o01 | Typhoon OS Voice Data |
| obw | Superior Drummer Sound File |
| obw | Toontrack Superior Drummer Audio |
| ocdf | OneClickDigital Audio Book |
| odd | Coby Voice Recorder Data |
| odm | OverDrive Media Data |
| ofg | OptimFROG Lossless Audio |
| ofr | OptimFROG Lossless Audio |
| ofs | OptimFROG Dualstream Audio |
| oga | Ogg Vorbis Compressed Audio |
| ogg | Ogg Vorbis Compressed Audio |
| oggstr | Godot Engine OGG Audio Data |
| ogx | Ogg Vorbis Compressed Audio |
| okt | Oktalyzer Music Module |
| olv | OnLive! Traveler Sound |
| oma | Sony ATRAC3 Compressed Audio |
| omg | Sony ATRAC3 Compressed Audio |
| omg | Sony OpenMG Audio |
| oml | OtsAV Media Library |
| omx | OtsAV Media Library Information |
| opm | FM Operator Type-M Voice Data |
| opu | Opus Audio File |
| opus | Opus Audio File |
| orc | CSound Orchestra Midi Audio |
| orc | TRS-80 Orchestra-90 Audio Data |
| orc | Voyetra Digital Orchestrator Pro Song |
| org | Organya Music Data |
| org | Sound Blaster Pro Organ Audio |
| organ | GrandOrgue Organ Sample Set |
| osb | Sega Dreamcast OSB Audio Data |
