Sync,
then run
untethered.

The model: iPhone configures, Watch plays

The iPhone is Run2Beat’s configuration and processing hub: it stores your library, computes BPM, measures loudness, builds BPM lists and pre-renders any tempo-shifted variants. The Apple Watch is a playback runtime — it stores the synced files and plays them back, nothing more.

Everything you see on the Watch is the result of an explicit sync from the iPhone’s Sync screen.

Manual and visible

There is no hidden background sync. You start it yourself from the iPhone’s Sync screen, where the app shows you exactly what’s new, updated or deleted before you commit. While the sync runs the iPhone shows a live overlay with progress; the Watch screen shows nothing during the transfer — that’s normal.

The two devices need to be active at the moment you start a sync. After that, both screens can be off — the transfer keeps running over Bluetooth in the background.

What gets transferred

For every track in a BPM list or standard playlist Run2Beat sends:

• The audio file, transcoded to HE-AAC for compactness on the watch.
• Title, artist and artwork embedded in the file’s metadata as a fall-back so the playlist is reconstructable even if the structured payload arrives late.
• BPM and loudness data (LUFS, true peak) so the Watch player applies the same gain math as the iPhone — the same track sounds equally loud on both devices.
• For BPM lists: pre-rendered tempo variants. The iPhone applies the recipe’s rate change with pitch preservation up front, so the Watch never has to do that work itself.
• The play order and the list metadata.

Equalizer presets sync separately via the Watch app’s shared settings channel. On the Watch you pick a preset directly from the Home view to change sound profile without your phone.

Speed and time expectations

Files are sent over Bluetooth. That’s a Bluetooth-shaped pipe - a normal-length playlist routinely takes several minutes to transfer for the first time. Subsequent syncs are much faster because Run2Beat only transfers what’s actually new or changed; lists and tracks that are already on the Watch are skipped.

If you re-open the Sync screen without having changed anything, the next sync completes almost immediately - the iPhone verifies the Watch is already in the desired state and skips the transfer machinery entirely.

Practical tips for fast and reliable syncs:

• Keep iPhone and Watch close together. Bluetooth degrades quickly with distance and obstacles.
• Wear the watch or leave it charging. Both devices need to be awake at the moment sync starts. After that they can both go to sleep.
• iPhone keeps syncing in the background. Lock the screen, switch to another app - the transfer continues. The overlay updates the next time you return to Run2Beat.
• Plan ahead for first-time syncs of large lists. Sending new tracks to the Watch always takes time; syncing tonight for tomorrow morning’s run goes a long way. Re-running the sync later with no changes is effectively instant.

Cancel any time, resume later

The Sync screen has a visible Cancel control while a transfer is in flight. Cancelling is safe — the next sync simply picks up what’s still missing. The pending-change indicator on the Sync screen tells you exactly what hasn’t made it across yet.

Standalone playback on the Watch

Once a list is synced, the Watch can play it back without the phone. You pair your AirPods directly to the Watch, open Run2Beat on the wrist, pick a BPM list or playlist and press play.

The Watch player honours the same volume normalisation, the same EQ preset and the same crossfade behaviour as the iPhone — the audio decisions are baked into the synced files and metadata, so the sound is identical regardless of which device you’re listening from.

If something doesn’t arrive

The Sync screen surfaces an item-level pending list and explicit error messages. Common situations:

• “Watch not reachable”. The Watch app isn’t open in the background or the devices are out of Bluetooth range. Open the Run2Beat app on the Watch once to bring the connection back up; sync will then start normally.
• A list is never half-synced. If a transfer is interrupted - low battery, the Watch leaves range for a long time, you cancel mid-sync - Run2Beat verifies on a per-list basis that both the list’s metadata and every audio file actually landed on the Watch. Lists that don’t pass that check within the sync window are removed from the Watch and queued for a fresh transfer on the next sync. You never end up with a list that looks playable on the Watch but is missing some of its files.
• “On Watch” badge. After a successful sync each list shows a green “On Watch” indicator confirming the Watch holds both the list’s metadata and every one of its audio files.

Storage on the Watch

Audio files transfer to the Watch’s app sandbox as HE-AAC. A typical 4-minute song occupies roughly 2 MB at 64 kbps HE-AAC — about half the size of a comparable-quality MP3 or AAC-LC file. That means a multi-hour BPM list still fits comfortably alongside other Apple Watch content on a modern watch.

Privacy reminder

Audio files are transferred directly from your iPhone to your paired Apple Watch using Apple’s WatchConnectivity framework. No data passes through Run2Beat’s servers because Run2Beat doesn’t run any.