Stream Lossless from a NAS: WebDAV, the Cache, and When the NAS Sleeps | Sleeve

The short answer

Yes. Sleeve connects to a network share at home over WebDAV — Nextcloud, Synology, QNAP and most NAS boxes — and plays FLAC, ALAC, AAC, MP3, WAV and AIFF from it as they are, with nothing re-encoded and nothing copied to the phone. What you have played from that share is kept in a local cache, so playback survives a Wi-Fi drop or a NAS that went to sleep. You choose the cache size, see what it is using, and clear it in Me → Cache whenever you want. Connecting one source is free and does not expire; Pro only raises the limits on how many sources and smart playlists you can have.

Why you're considering NAS streaming at all

If your music already lives on a NAS, you are not deciding whether to store it there — you decided that years ago. What you are deciding is how the iPhone is allowed to reach it. The options are narrow: either the files come to the phone and eat its storage, or the phone goes looking for them every time you press play, over a network that might be asleep.

That second option is where the real questions live. A NAS is a machine with a power button and a disk that spins down when it thinks nobody is listening. Home Wi-Fi has dead zones, a router that reboots, and neighbours' microwaves. If streaming means one stutter per album because the box took nine seconds to wake, the whole arrangement fails on the first evening and you go back to copying files. If streaming means everything you care about is already on the phone, you did not need a NAS.

So the real question behind "can it stream FLAC from my NAS" is: what happens in the fifteen seconds after the network is not there? Everything below is about that.

How the streaming actually works

There is no import step and no sync step. Sleeve is pointed at a WebDAV share the same way it is pointed at a folder in Files, and it reads the files where they sit — audio moves only between the share and your device, for the purpose of playing it. It never uploads your files and never mirrors the library to a server.

The audio path over the network is the only part that touches your NAS, but it is not the only part of playback that changes when the source is remote. The things that make a NAS library pleasant rather than merely functional are the same whether the bytes came from a disk or from a share:

• Nothing is re-encoded. FLAC, ALAC, AAC, MP3, WAV and AIFF are decoded by iOS and played as they are.
• Gapless across an album, so a live record stays one performance instead of gaining a gap between tracks.
• ReplayGain, so tracks pulled from different sources sit at the same loudness — the normalisation data lives in the file's tags, so it survives the trip from the NAS.
• Format, bit depth and sample rate stay on screen. A 24/96 FLAC says 24/96, which is the only way to know that a stream off your share is really the hi-res file and not something you assumed it was.
• A ten-band equalizer, applied after decode, so it does not care where the bytes came from.

One limit is worth stating plainly, because it is the kind of thing streaming pages gloss over: Sleeve relies on the codecs iOS provides and cannot add codecs that iOS does not provide. In return it reports plainly when a file cannot be decoded rather than failing silently. So a file your NAS serves that the system will not decode produces a clear message, not a stutter.

What happens when the NAS sleeps

There are two different situations people lump together, and they behave differently.

The Wi-Fi drops mid-album. What you have already played from a cloud drive or a network share is kept in a local cache, so it keeps playing off Wi-Fi. The album does not stop because the router hiccuped.

The NAS is off, asleep, or you are out of range. A source can become unavailable for reasons outside Sleeve's control — a machine powered off, a network change, an expired authorisation. Sleeve tells you which source is affected and what to do about it, but it cannot restore access on your behalf. What it will not do is fail quietly.

There is one honest limit to the cache that competitors rarely spell out: the cache fills from what you actually play. It is not a mirror you can point at an album and pre-fill, so the first play of an album you have never heard is still a network play. In exchange, the cache costs you nothing until you press play, and you decide its ceiling rather than discovering its growth. A phone with 128 GB free and a cache set to 4 GB holds roughly 1,700 lossless CD-quality tracks — about 1 GB for an album, a few tens of megabytes for a single hi-res track — which is why the size is yours to choose and visible while it fills. The Sources view shows each source's own online state and offline footprint in plain sight, so "how much of this album is on my phone" is a thing you can check rather than estimate.

If you need a guarantee rather than a cushion, a USB stick or SD card in the Files app is the alternative: it is one of the four source kinds too, it costs no network at all, and it sidesteps both the sleeping NAS and the dead router. It also costs storage on the phone, which is exactly the trade the other way.

What you are paying for

The free tier connects one source and allows two smart playlists. Streaming lossless audio from it is not a Pro feature. Neither are gapless playback, ReplayGain, the equalizer, lyrics, artwork or tag editing — the free tier does not expire and will not begin showing ads, which the terms make a commitment rather than a promotion. There is no advertising and no tracking SDK of any kind in the app.

Pro lifts the two limits and nothing else: as many sources as you like, as many smart playlists as you like. It is available yearly, or once and never again as a Universal Purchase across iPhone and iPad. So if your music is in one place — one NAS, one share — you never need to pay to stream it. You need to pay the day you decide the library is really four places: NAS, phone folder, cloud drive, and the old laptop.

How this compares to the obvious alternatives

Mounting the share in the Files app and streaming it from there sounds identical, but on iOS the share would have to be mounted as a WebDAV location, and the music player most people install on top of it is built around files it owns. It also gives you no way to see what is cached. Syncing the NAS to the phone with a third-party app does solve the network problem, but it costs your phone's storage, moves bytes over metered mobile data when you are out, and leaves a second copy to fall out of sync with the first.

AirPlay is not an alternative, it is a different thing: it routes what the phone is already playing to a speaker. Streaming apps that "support your NAS" usually mean they transcode it, which is precisely the opposite of lossless.

What Sleeve does differently

• It reads your files in place. Connecting a source costs you no storage, and your library never drifts from the originals. See how Sleeve handles your files.
• It does not re-encode. A 24/96 FLAC from the NAS plays as a 24/96 FLAC, and the format, bit depth and sample rate stay on the playback screen instead of two levels down.
• The cache is yours. You set its size, watch it fill, and clear it whenever you want.
• It tells you when it cannot play something. Undecodable files and unavailable sources are reported, not swallowed.
• It never uploads your music. No account, no tracking SDK, source credentials in the Keychain. See the Sleeve privacy policy.

The limits are equally real: WebDAV only — SMB is not offered; one source on the free tier; the cache fills from playback, so a cold album is still a network play; and the decode is whatever iOS can decode, which rules out formats iOS does not support.

The decision

A NAS-based library on iPhone works if two things are true: the box speaks WebDAV, and you are honest that you want a library, not a second copy of one. If you want the second, a sync app is the honest tool. If you want the first, Sleeve reads what you already own, streams it losslessly over the network, keeps what you have played on the phone, and tells you plainly when it cannot.