oTAPE · The open digital cassette format

oTAPE 1.0 · open specification · release candidate Press record.Mean it. oTAPE is an open file format for digital cassettes. One .otape file holds a whole tape: two sides of fixed length, each one continuous recording, plus the label, the J-card and the record tabs. It's self-contained and works offline. Extension.otape ContainerZIP + JSON LicenseCC BY 4.0 Shell Ferro Black Drawn in your browser from a few lines of appearance JSON. The reels follow the spec's tape-pack model. 01 The idea The slow way,on purpose. Making a mixtape used to take an evening. You picked every song, sat through the recording and wrote the titles by hand. oTAPE is a file format that keeps those constraints. It isn't a new codec or a music player: it describes a whole cassette. 01 A cassette,not a playlist. Each side is one continuous take. The silence between songs, a spoken intro, the clunk of the pause button: it's all part of the recording. Track markers can name the songs without splitting the side. 02 It behaveslike tape. A fixed length, two sides on one tape, and a position you reach by winding, not jumping. Play side A to the end, flip the cassette, and you're at the start of side B.

03 The file isthe object.

Audio, label, J-card, booklet and history all live inside one .otape. It never links back to the MP3s it was recorded from, or to anything online. 04 Listeningis read-only. Playing a tape never changes the file. The player remembers your place separately, the way a real tape stays wound where you left it.

05 Open andsimple.

A ZIP archive, one JSON manifest, AAC audio, PNG or JPEG artwork. Every part is a standard format you can open with existing tools. 06 Each tape hasits own look. Supply artwork at exact physical proportions, or describe the shell and label in a few lines of JSON that any player can draw.

02 Try it Put a tapein the deck.

This is the oTAPE Web Deck: about 1,200 lines of plain JavaScript, no libraries. It comes loaded with Gitsem, a C10 single that Mirat Can Bayrak wrote at 24 and recorded again at 42, and plays any .otape you drop here.

Files stay in your browser and are never uploaded.

A cassette never sounded the same in two players.

oTAPE players can now play a tape the way a machine of the era would have: a studio deck, a car stereo, a portable stereo that has seen better days. The sound changes on its way to your speakers. The file stays exactly as it was recorded.

oTAPE Tape sound selector  TS-6 −1 % 0 +1 % Speed+0.00 % Pitch over the last five seconds How it's done WobbleNo motor turns perfectly evenly.

A slow drift in speed bends the pitch (wow), a fast shiver roughens it (flutter). The player reads the music a hair early or late, moment by moment, so the pitch wanders just as much as it did on that machine. HissEvery tape has its own bed of noise. It runs while the tape runs, between songs and over blank tape too, and stops the moment you press stop. WarmthRecord a tape hot and it rounds off the peaks, the treble first. That gentle squeeze is a big part of why cassettes sound warm. WearOld tape loses its top end, drops out for a split second where the coating has worn thin, and a head knocked out of line smears the stereo picture. Nothing is baked in. The machine is applied while you listen. Your .otape file isn't touched, recordings stay clean, and you can switch machines in the middle of a song.

Machines are files.

Each one is a small open preset, an .otsound file, written in real-world units: percent of speed, decibels, hertz. So a portable stereo sounds the same in every oTAPE player. Six come built in; make your own and share it. 04 Inside the file Unzip acassette. An .otape file is an ordinary ZIP archive with a fixed layout: a mimetype entry first, so tools can identify the file without unzipping it, then the manifest, one audio file per recorded side, and optional artwork and documents. night-drive.otapeZIP mimetype application/vnd.otape.cassette manifest.json the cassette, sides A and B, the look audio/ side-a.m4a AAC-LC, one continuous take side-b.m4a omitted while the side is blank artwork/ optional, fixed physical sizes cassette-face-a.png label-a.png jcard-front.jpg jcard-spine.png booklet-01.png … docs/ booklet.html, notes.md manifest.json · a blank C60 { "format": "oTAPE", "format_version": "1.0", "cassette": { "id": "550e8400-e29b-41d4-a716-446655440000", "title": "Night Drive", "type": "C60", "side_length_seconds": 1800, "created_at": "2026-10-28T22:00:00Z" }, "sides": { "A": { "write_protect": "intact", "audio": null }, "B": { "write_protect": "intact", "audio": null } } } Media typeapplication/vnd.otape.cassette Apple UTIorg.otape.cassette AudioAAC-LC in M4A, which every player must support. ALAC, FLAC and PCM are optional. TimelineInteger frames at 44.1 or 48 kHz, exact to the sample MagicPK\x03\x04 at offset 0, the media type at byte 38 VersionsMAJOR.MINOR. Minor versions only add optional fields, and unknown data is preserved. 05 The medium Fixed length.Breakable tabs. A cassette's limits shape what goes on it, so oTAPE keeps them. You choose a length before you record, and each side has a record tab you can break off. Pick a length C4623 min / side · 65.7 m · 18 µm C6030 min / side · 85.7 m · 18 µm C9045 min / side · 128.5 m · 12 µm C12060 min / side · 171.4 m · 9 µm C74 Custom: minutes per sideA custom tape is named like a real one: C plus its total length in minutes. Tape length and thickness follow the reel model in Appendix B.3 of the spec. Snap the tab AB Recording allowed: This isn't DRM. Like the tab on a real cassette, it protects a finished tape from being recorded over by accident, and anyone can tape over the hole. 06 The paper Artwork,to the millimeter. Shell and label artwork, the J-card's front, spine and back flap, a fold-out booklet, liner notes and a dedication. Every image slot has a fixed size in millimeters, so artwork made in one app fits correctly in any other. flap 25.4spine 12.7front 63.5 mm SlotmmRecommended px Cassette face A / B100.4 × 63.82410 × 1531 Label A / B89.0 × 42.02136 × 1008 J-card front63.5 × 101.61524 × 2438 J-card spine12.7 × 101.6305 × 2438 J-card back flap25.4 × 101.6610 × 2438 Booklet panel63.5 × 101.61524 × 2438 Thumbnailsquare1024 × 1024 24 px/mm recommended, 12 px/mm minimum, aspect ratio within ±1%. Shell and label images must be transparent over the window and hub holes, so the player's reels show through.

07 The reference app oTAPE Studio.

A three-piece hi-fi for your Mac: the SP-2 CD/MP3 source player and the TU-01 internet radio tuner, both wired into the OT-1 cassette deck. Load your music or tune in a station, press REC, and the tape records in real time.

Pause the player and the deck records silence.

Blanks and a designerC46 to C120 blanks with working tape counters and reels. The designer covers the shell, label, lettering, J-card, artwork and record tabs, starting from eight presets.

Save, and you have an .otape file.