How to Use SynchCast

Install & Launch

On Windows: install SynchCast from the Microsoft Store. Because it uses Windows' own audio engine, there are no virtual drivers to install and no administrator rights to grant. It installs per-user in under a minute, so it works even on a locked-down or managed PC.

On a Mac: download SynchCast from this site, open the file and drag SynchCast into your Applications folder. The first time you start it, macOS asks for permission to record system audio — allow it. That permission is the whole trick: it is how SynchCast hears what your Mac is playing, with no extra drivers.

Connect Your Devices

Pair your Bluetooth headphones or earbuds, or plug in your wired speakers, just like you normally would — through Windows' Bluetooth and sound settings, or macOS's System Settings. Make sure your computer recognises every device you want to use before opening SynchCast: the app lists whatever your system already sees as an available output.

Start Broadcasting

Open the SynchCast application. You will see a list of all available audio outputs. Simply check the boxes next to the headphones or speakers you want to broadcast to, and click Start. Play a movie or music on your PC, and it will instantly play on all selected devices in perfect sync! Each device gets its own volume slider, and new devices you plug in or pair mid-session appear automatically — no restart needed.

Fixing Bluetooth Lag with the Delay Slider

Bluetooth audio has a small built-in transmission delay, so a Bluetooth speaker or headset can sound slightly behind a wired device playing the same source. If you notice an echo between two devices, open that device's delay slider in SynchCast and nudge it up in small steps until the sound lines up. Wired devices auto-compensate by +100ms whenever a Bluetooth device connects, so most setups need little or no manual adjustment.

How Many Devices Can I Add?

Up to about 5 at once. There's no artificial cap in the software — each device gets its own dedicated render thread — but real-world Bluetooth radios and USB audio stacks start struggling past roughly 5, so that's the honest number for glitch-free playback. Most people run 2–3. How many Bluetooth devices specifically will stay clean depends on your PC's Bluetooth radio, and SynchCast will tell you roughly how many yours can drive.

Running It in the Background

Once broadcasting, you can minimize SynchCast to the system tray and it keeps every device in sync in the background — you don't need to keep the window open on top of your movie or game.

SynchCast vs. Windows' Built-in Options

Windows has two of its own ways to do this, and it's worth knowing why they behave differently. Stereo Mix (Sound Control Panel → Recording → Properties → Listen) works on some sound cards and not others, and it adds a fixed processing delay that you can't adjust — so the two outputs usually land noticeably apart and you hear an echo.

Windows 11's Shared Audio is a genuine first-party feature and worth trying first if you have it: open Quick Settings and you can send audio to two Bluetooth devices. But it needs recent hardware (it shipped on Copilot+ PCs and newer Bluetooth stacks), it's limited to exactly two devices and both must be Bluetooth — so it can't include your laptop speakers or a wired pair.

The difference that matters for a long session is drift correction. Both Windows options line devices up once; neither keeps correcting as the devices' clocks diverge. SynchCast measures the divergence continuously and resamples to compensate, which is why it holds sync over a whole film rather than the first few minutes. There's a full side-by-side of all four options — including VoiceMeeter and Virtual Audio Cable — in this comparison.

Choosing Which Devices to Prioritize

When you're running three or more outputs, the order you add them isn't arbitrary. Add your wired output first if you have one — it has almost no latency, so it makes the most stable reference for everything else to be aligned against.

Then add Bluetooth devices in order of how much you care about them. If your PC's Bluetooth radio starts running out of bandwidth, the symptom is stuttering on the most recently added device rather than everything degrading equally, so put the pair you're actually listening on earlier in the list.

Mixing codecs is also worth being deliberate about. Two identical earbuds behave predictably; one AAC device and one SBC device start from very different baseline delays, so expect to use the per-device delay slider rather than assuming the defaults will match.

A device isn't showing up in the list

SynchCast only lists outputs your computer itself already recognises. Pair the Bluetooth device (or plug in the wired one) in Windows' Bluetooth and sound settings, or in macOS System Settings, confirm it shows up there, then reopen SynchCast's device list.

Mac: “macOS is blocking audio capture”

SynchCast needs permission to record your Mac's system audio. Open System Settings → Privacy & Security → Screen & System Audio Recording, turn SynchCast on, then press Start again. The button in the app's banner opens that page for you.

If macOS says it can't verify the developer the first time you open SynchCast, go to System Settings → Privacy & Security, scroll down and click Open Anyway. You only need to do this once.

Activating your license after purchase

After buying a lifetime license, you'll get a license key by email. Open SynchCast, go to Settings → License, and paste the key in to activate. A license is valid on one computer at a time — use the Release this seat button before moving to a new machine.

Audio still sounds slightly out of sync

If the drift correction is holding but the two devices still sound a fraction apart, what's left is the fixed baseline delay between them — and that's what the per-device delay slider is for. Drift correction stops the gap from growing; the slider sets where the gap starts.

A worked example. Say you're running laptop speakers plus AAC earbuds, and the earbuds sound late. Play something with a sharp, repeating transient — a metronome, or any track with a clear hi-hat — and raise the delay on the speakers (the faster device) rather than lowering it on the earbuds, since you can only ever add delay, not remove it. Move in 20 ms steps: at some point the two stop sounding like two sources and collapse into one. Typical AAC earbuds need somewhere around 150–200 ms of speaker delay to match; SBC often needs more.

Set it once per pair of devices and it stays right — the value depends on the hardware, not on the session, so you shouldn't need to touch it again for that combination.

System requirements

Windows 10 and Windows 11. SynchCast uses Windows' built-in WASAPI loopback, so no drivers, no Virtual Audio Cable and no admin rights are needed at any point.

macOS 14.2 (Sonoma) or later, on Apple Silicon and Intel Macs. It uses the system-audio capture macOS added in 14.2, which is why older versions can't run it — and why no extra audio driver is needed.

Linux isn't supported.