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Cassetteur plays the music you own, album by album, from a folder on your iPhone or on a drive you plug into it.

What you need

• An iPhone with iOS 26 or later. Cassetteur is made for iPhone; there is no iPad version.
• Music files you own: FLAC, MP3, AAC or ALAC (.m4a), WAV, AIFF, and DSD (.dsf, .dff), one folder per album.
• If you like: a USB‑C drive or card for your library, and a USB DAC.

Choosing your music folder

The first time you open Cassetteur, tap Choose Library… and pick the folder that holds your albums: a folder on a USB drive, in On My iPhone, or in iCloud Drive. Each album is a folder of tracks inside it. An empty folder is fine: tap Import Music… to copy albums in from the Files app.

Settings is the page to the left of your library: swipe right to reach it (or press ⌘, on a keyboard). To use a different folder later, go to Settings → Library → Change Library… (Import Music… is there too).

“Waiting for your music drive…”

Cassetteur remembers the drive your library is on. If you open the app while that drive is not plugged in, it waits for it rather than asking you to choose again. Plug the drive in and your library opens by itself. To use another folder instead, tap Choose a different library…

If you unplug the drive while music is playing, the few seconds already read keep playing, then Now Playing shows Waiting for the library… and the music carries on from the same place when the drive is back. Tapping another album while the drive is away stops the music and shows “Can’t play this album — the drive isn’t available”.

DSD, DoP and USB DACs

Cassetteur plays DSD files everywhere. By default it converts them to high-resolution PCM, so they play on the iPhone’s speaker, on headphones, or through any DAC. If your USB DAC accepts DSD over PCM (DoP), you can send it the original DSD instead. Plug it in, open Settings → Playback → Output, tap ⓘ beside the DAC, and turn on Play DSD as DoP. Cassetteur first asks you to confirm that the DAC, and whatever it feeds, has a safe volume control.

DoP has to reach the DAC at full digital level, so keep the iPhone’s volume at maximum and set the level with the DAC’s own volume. On the same screen, Verify… checks whether your DAC’s own volume works with DoP (unplug any headphones from the DAC first); once it has passed, DoP keeps playing when you turn the iPhone’s volume down. When DoP isn’t possible, for example with the iPhone’s volume below maximum on a DAC that hasn’t passed, Cassetteur plays the album converted instead.

A USB DAC’s screen also has Bit-perfect output, which bypasses the system mixer and its volume. The iPhone’s speaker, Bluetooth headphones and AirPlay have nothing to set.

Keyboard

With a keyboard connected you can use Cassetteur without touching the screen. The arrow keys move, Return plays (hold it for an album’s options), Esc goes back, ⌘P opens Now Playing, ⌘S searches and ⌘, opens Settings. Press ? to see every shortcut for the screen you are on. You can change any of them in Settings → Input devices → Keyboard shortcuts.

Game controllers

A game controller works too. The D-pad moves, ✕ (A) plays (hold it for an album’s options) and ○ (B) goes back. △ (Y) opens Now Playing, the shoulder buttons go to the previous or next album, the triggers to the previous or next track, and holding □ (X) dislikes the track that’s playing. Change what each button does in Settings → Input devices → Controller.

Turning online lookups off

Cassetteur fills in album names, years and covers by asking MusicBrainz, AcoustID, the Cover Art Archive and Apple. It never sends your music. To stop it, go to Settings → Album details and turn off Look up album details online. The choice is saved in your library, so it applies on every device that opens it. The privacy policy lists exactly what each service receives.