Support
What is Offstem?
Offstem is a paid iPhone app (A$4.99, one-time purchase — no subscription, no in-app purchases, no trial) that splits a song or video into four stems: vocals, drums, bass, and other. It runs entirely on your device — no account, no upload, no server. Your audio never leaves your iPhone.
Requirements
- iPhone running iOS 17 or later.
- ~135 MB of free space for the machine-learning model (required — it does the separating).
- A Wi-Fi connection on first launch to download the model (downloads are Wi-Fi-only by default and resumable).
Frequently asked questions
Is it really offline?
Yes. Separation runs on-device with a Core ML model. The only network use in the entire app is the one-time model download on first launch. After that, Offstem works in Airplane Mode.
Why is the app so big?
The separation model is ~135 MB. It's the price of doing studio-quality stem separation without a server. The app itself is small — the model is downloaded once and reused for every separation.
What formats can I import?
Audio: M4A, MP3, WAV, AAC. Video: MP4, MOV (the audio track is extracted; video frames are not retained).
Can I use my own music?
Offstem is a tool for working with audio you own or have the rights to use — remixing your own tracks, practicing, karaoke, education, and sampling material you have rights to. Please only process audio you're allowed to use.
How do I delete my separations?
In the Library, open a job's ⋯ menu (or swipe left) and choose Delete. This removes the stems and the original file from your device. Deleting a job permanently deletes those files — there is no undo.
Why can't I play a stem after separating? / Playback is silent.
Try pausing and playing again, or opening the Mixer. If a stem loads but is silent, restarting the app usually restores audio. If it keeps happening, tell us (details below).
How do I get a refund?
Purchases are handled by Apple. Request a refund through reportaproblem.apple.com with your Apple ID — Apple decides refunds for App Store purchases.
Reporting a bug
Please include:
- iOS version (Settings → General → About → iOS Version).
- iPhone model.
- What you were doing when it happened (which screen, which song — and whether it was audio or video input).
- Whether it happens every time or intermittently.
- If possible, the song length and file format.
That's everything we need to find it — send it to support@offstem.app.