What works offline after the first download
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Part of the guide: On-Device Voice Guide
Syllivo works offline after the first download. That sentence needs unpacking, because "offline" is often claimed loosely. This is what an offline voice generator means in practice for Syllivo: once a voice's files are on your device, generation itself needs no internet at all. But two things still need a connection, and pretending otherwise would be dishonest: the first download of a voice's files, and app updates. Everything below separates the two lists cleanly.
What works with no internet
- Generating speech from a script with a voice that is already installed on your device.
- Playing back audio you have already generated.
- Opening your saved projects and their jobs, and resuming a job from its completed sections.
- Pausing, stopping, and resuming generation — completed sections stay saved on your device.
- Switching between voices that are already installed, and changing generation settings for a new job.
None of this sends your script or audio anywhere, because generation happens in your browser with files that are already on your device. That is also why the app keeps working on a train, on a weak connection, or with mobile data off — once the files are there, the connection is irrelevant to the job itself.
What still needs the internet
- The first download of a voice's files. A voice you have never used yet cannot generate until its files download and are verified. That download happens automatically the first time you generate with that voice, with real progress shown.
- App updates. The weekly update check and the Update button in Settings need a connection to fetch a newer version, and they only reload the app when a newer version actually exists.
- Any voice you have not downloaded yet. Each voice set downloads separately, so installing one voice does not make the others available offline.
Phone storage reality
Voice files live on your device, so they take up storage there. Custom Voice is the largest of the three engines, and Quality and Fast are smaller — if your device is nearly full, free up space before downloading a new voice, or generation may fail for lack of room. Browser storage can also be erased by the browser itself, so download finished audio you want to keep rather than treating the browser as permanent storage. For the full picture of how the files get there, see how on-device voice generation works, and for the free-versus-hosted trade, see free AI voice generator: what free actually means.
Frequently asked questions
Can I generate on a flight with no connection?
Yes, if the voice is already installed on your device. Open the app, pick an installed voice, and generate. A voice you have never downloaded cannot generate until its files download, which needs a connection.
Do I need the internet to resume a paused job?
No, as long as the voice is installed. Completed sections are saved on your device, and Resume continues from the next unfinished section without downloading anything again.
Why does the first generation with a new voice need the internet?
Because the voice's files are not on your device yet. The first generation downloads and verifies them, then generates in the same flow. Every later generation reloads those saved files instead of downloading again.
What happens if I update the app — do my downloaded voices disappear?
No. Updating never deletes downloaded voices. After an update, generating with an installed voice loads the saved files instead of downloading them again.