One phone,
the whole chain.

Your OneDrive music, in your phone’s library

In Settings > Music folders · network · cloud, tap Add cloud storage, sign in with your Microsoft account and pick a music folder. Its songs join your phone and NAS music as albums, artists, tracks and folders.

• Plays right away — songs stream without downloading first, and you can jump to any point in a track.
• Keep songs on the phone — download tracks, albums or folders to play them offline. Once a download finishes, the copy on the phone is what plays.
• Read only — CastFi reads only the music in the folders you pick and never changes or deletes files in your cloud. Songs come straight from Microsoft to the phone, never through a CastFi server.
• Mobile data — in Settings > Mobile data, streaming and downloads/sync each have their own switch. Out of the box only streaming is on; downloads and sync wait for Wi-Fi.

Your NAS library becomes this phone’s library

Add a NAS or Windows shared folder in Settings > Music folders · network storage and its music sits next to your phone’s folders as albums, artists, tracks and folders. No PC needs to be on, and any brand works (SMB2 or later).

• Untouched — FLAC goes bit-perfect to a USB DAC and DSF plays as native DSD, with DSD upsampling and headphone correction as usual.
• Tens of thousands of tracks — read once, then only changes are re-read, quietly in the background so playback never stutters.
• Keep songs on the phone — download tracks, albums, artists or folders to play them when the NAS is out of reach. Downloads resume, and nothing shows up twice.
• Views — pick All, This phone or NAS from ‘View’ in My music.
• Sign-in stays on the phone — if you choose to save it, it is encrypted in the phone’s secure storage and sent nowhere. Connections are direct, on the same Wi-Fi (or a VPN you set up).

Another phone’s or DAP’s music, as if it were yours

Turn on Settings > Remote & sharing > Share this phone’s music on the phone or DAP that holds the music, and another CastFi device on the same Wi-Fi can pick it in My music and browse and play it like a PC library. No copying files around.

• Browse — albums, artists, tracks, folders and search, with album art.
• Play here — the original file streams in and goes through your correction, DSD upsampling and USB DAC.
• Play there — pick a track and the device that holds it plays it, with this phone as the remote.
• Off by default, home only — only devices you turn on, and only connections from your private home network. File paths stay hidden, and nothing goes through an outside server.

Only the folders you chose

You pick the folders that hold your music, and CastFi reads only those. Call recordings and voice notes never end up in the library. Remove a folder and its tracks leave the list — the files on your device stay where they are.

• Albums, artists, tracks, folders — organised, with the sort you choose (recently added, name, year…) remembered, album/artist grids and fast scrolling for long lists.
• Phone folders + NAS + cloud — your phone’s folders, network storage and cloud storage (OneDrive) together, split by ‘View’ into All, This phone, NAS or Cloud.
• De-duplicated — the same track in several places is shown once.
• Playlists — created on the phone, saved, and still there after a restart.
• Big libraries — built to hold up at tens of thousands of tracks.

Your files need not be DSD already

Common formats such as FLAC and WAV are converted to DSD on the way out. You need not hunt for DSD releases — your whole library takes the same path.

• Automatic rate — as high as the DAC accepts, weighed against the headroom the phone has.
• It says so when headroom runs out — it does not quietly downgrade and move on.
• Output policy first — while upsampling, the DSD output policy takes priority.

Once it sounds correct, add what you like

Correction is the step that makes it right; what you add on top is a separate set of controls, named in plain language with no numbers to wrangle.

• Taste controls — bass, vocals, clarity and air.
• Space and effects — BASS+, CLEAR+, WIDE+, speaker space and crossfeed.
• Volume ownership — the DAC’s own volume when it has one, the app’s when it does not.
• Level compensation — perceived loudness stays put when settings change.

The things you actually use while listening

• Lock screen and notification controls — operate without waking the screen.
• DAP buttons and remotes — play, next and previous from a DAP’s hardware keys, wired earphones or Bluetooth remotes.
• Home widget — now playing and transport, right on the home screen.
• Tablets and foldables — list and player side by side on a wide screen.
• 12 languages — including Korean, English and Japanese, switchable in settings.