| ocdf | OneClickDigital Audio Book |
| odd | Coby Voice Recorder Data |
| ofg | OptimFROG Dualstream 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 |
| osb | Sega Dreamcast OSB Audio Data |
| osp | Orion Sampler Program |
| ots | OtsAV Album |
| ots | OtsJuke Audio |
| out | Atari Jaguar Parsed MIDI Audio |
| p | AKAI S900 Program |
| p | Pulsar Audio Data |
| p00 | Roland V-Synth Patch Data |
