---
title: "Sync Video Playback Across Devices | sync.video"
description: "Play one video in step on phones, laptops, tablets and TVs: each opens its own copy, joins a room by code and stays in sync. Free, peer to peer, no upload."
url: https://sync.video/sync-player
---

Free · runs in your browser

# Play one video in sync on many devices

Every screen opens its own copy of the same file, joins a room with a short code, and plays, pauses and seeks together, to within a few milliseconds on a good network.

To play a video in sync on several devices, give each device its own copy of the same file, open this page on every one of them, start a room on one and join it from the others with the six-character code. From then on, play, pause and seek on the host happen on every screen at once, and each device keeps correcting itself so the picture stays together.

Nothing is streamed. The video never travels between the devices; only small play, pause and clock messages do, normally straight from device to device. That is why it works with a 4K film over a modest connection, and why you need the file on each device first: copy it across, share it from a cloud folder or hand round a USB stick before you start.

People use it for [a watch party with friends in other homes](https://sync.video/watch-party), to split one picture over a [wall of screens](https://sync.video/video-wall), for [a silent disco on everyone’s phones](https://sync.video/silent-disco), and in classrooms, churches and galleries where several screens should show the same thing. If a device’s sound is late because of Bluetooth or a soundbar, [measure its delay](https://sync.video/audio-delay-test) first and set it once.

How devices agree on time: a guest pings the host, the host stamps its clock, and from the four timestamps the guest works out the clock difference and the trip time. Many pings, keeping the fastest, make it precise.

Sync player

## Everything in sync player

### Watch together

* [ Host a watch party with your own files Friends in different homes, one film, the same moment on every screen. ](https://sync.video/watch-party)
* [ Host a movie night on Discord Go Live, Watch Together, or a full-quality copy on every screen with Discord for voice. ](https://sync.video/discord-watch-party)
* [ Compare Syncplay, Jellyfin SyncPlay and this Local-file group watching without a desktop player, a media server or a library. ](https://sync.video/syncplay-alternative)

### Screens and events

* [ Make a video wall from phones, tablets or TVs One picture split over a grid of screens, with gaps for bezels and every tile in step. ](https://sync.video/video-wall)
* [ Run a silent disco on guests’ phones Headphones on, one room code, and the same beat in every ear without renting a kit. ](https://sync.video/silent-disco)

## How to start a sync room

1. ### Open the same file on every device
On each device, drop the file onto **Drop the video to play in sync** (or **Open your copy of the video** on a device that is joining). Phones pick it from Files or Photos. It is never uploaded.
2. ### Start a room on the host
Press **Start a room**, choose **Who controls playback** (**Only me** or **Everyone**) and the **Sound** (**Every device** or **Only the host**), then **Create room**. The code, a QR code and **Copy link** appear.
3. ### Join from the other devices
Scan the QR code, open the link, or press **Join a room**, type the **Room code** and press **Join room**. Each device appears under **Devices** with **Same file** or **Different file** and its sync quality.
4. ### Play for everyone
Press **Play for everyone** (Space or K). Seek with ←/→ (Shift for 30 s), go **Full screen** (F), and use **Pause for everyone** or **Start again for everyone** as needed.

## How the devices keep the same time

Every device has its own clock, and no two agree exactly. So the first thing a guest does after joining is ask the host the time, many times over. Each question carries the guest’s own time when it left, the host stamps its time when the question arrives and again when it sends the answer, and the guest notes when the answer comes back. From those four times it can work out both how long the trip took and how far its clock differs from the host’s.

A single answer can be thrown off by a busy Wi-Fi network, so the guest keeps asking a few times a second and trusts only the quickest round trips, where there was no time for anything to get in the way. It also watches how the difference changes over minutes, because cheap clocks run slightly fast or slow.

### From a shared clock to the same frame

When the host presses play, it doesn’t say “play now”; it says “the film was at this point at this moment on my clock, playing at normal speed”. Every device turns that into “where should I be right now?”, compares it with the frame actually on its screen, and corrects. Small errors are fixed by playing a fraction faster or slower (between 0.3 and 3 per cent, too little to hear); a jump of more than about 300 ms is fixed with a seek. Each device reports how far off it is, shown as **Excellent**, **Good**, **Fair** or **Poor** next to its name.

## How close it gets, and what gets in the way

On a good home or office network, devices usually stay within a few milliseconds of each other, well under the length of one video frame. Over the internet, between homes, the clock is still accurate but each device has more to correct and the numbers move around more. What limits it in practice is rarely the network:

* **Bluetooth headphones and speakers** add their own delay, typically a large fraction of a second, after the sound leaves the browser. The picture is in sync but the sound arrives late.
* **TVs and soundbars** process the picture and the sound separately, which can shift either by tens of milliseconds.
* **Smart-TV browsers** vary a lot. Some play smoothly and correct well; older ones stutter when asked to change speed.
* **Busy or old devices** may drop frames on a high-resolution file. A smaller copy of the film plays more evenly.

The fix for the first two is the **Output delay** slider on each device. **Add the delay this browser reports** fills in what the browser knows about its own audio path, and **Remember this delay on this device** keeps it for next time. For anything the browser doesn’t know, such as a Bluetooth speaker, the host’s **Flash and beep test** makes every screen flash and beep on the shared clock so you can see and hear which one is late and nudge it with \[ and \].

## Each device needs its own copy of the same file

Because the video is never sent between devices, every device plays the file it already has. It has to be the same file, not just the same film: a different edit, a different frame rate or a copy that was re-encoded by a messaging app can have a few seconds more or less at the start, and the devices would then be in step with the clock but out of step with each other.

To catch that, each device makes a fingerprint of its file (its size, its length and a quick hash of three small slices) and the room compares them. A device shows **Same file** when it matches the host, **Different file** when it doesn’t, and **Same length, other file** when the length matches but the bytes don’t, which usually means a re-encoded copy that may still line up.

### Getting the file onto every device

* Copy it from a computer with a cable, AirDrop or Nearby Share, choosing the original quality rather than a compressed preview.
* Put it in a shared cloud folder and download it on each device before you start.
* For a fixed installation, keep the file on each player’s local storage so nothing depends on the internet during the show.

## Where a sync player earns its place

__Common set-ups and the settings that suit them__
| Use                            | Who controls playback | Sound               | Useful extras                                                                   |
| ------------------------------ | --------------------- | ------------------- | ------------------------------------------------------------------------------- |
| Watch party across homes       | **Everyone**          | **Every device**    | Share the code in your chat; see the [watch party guide](https://sync.video/watch-party)          |
| Classroom with several screens | **Only me**           | **Only the host**   | **Full screen** on each screen; one teacher controls                            |
| Church overflow rooms          | **Only me**           | One room’s speakers | **Start** **At a set time** so every room begins together                       |
| Gallery or shop window         | **Only me**           | As the space needs  | **Loop the video**; keep screens awake with full screen                         |
| Video wall                     | **Only me**           | **Only the host**   | **Video wall** with a grid; see the [video wall guide](https://sync.video/video-wall)             |
| Silent disco or dance class    | **Only me**           | **Every device**    | Each phone’s **Output delay** for headphones; see [silent disco](https://sync.video/silent-disco) |

Rooms hold up to 50 devices and last up to 12 hours. A device that drops off, or is reloaded, can rejoin the same room with the same code and picks up where everyone else is.

## Questions about playing a video on several devices

### Is the video uploaded or streamed to the other devices?

No. Each device plays its own copy from its own storage. Only short messages travel between devices: play, pause, the position, and the clock checks that keep them together. That is why every device needs the file before you start.

### Do the devices need to be on the same Wi-Fi?

No. Devices in different homes or countries can share a room. On the same network the direct connection is usually quickest and the sync tightest. If a network blocks direct connections, as some school and office networks do, the messages are passed through our relay instead and the room still works.

### How many devices can join one room?

Up to 50, including the host. Every guest connects to the host, so the host should be a reasonably capable device on a steady connection; a laptop on mains power is ideal for a big room.

### Can I use it with Netflix, Disney+ or YouTube?

No. It plays video files you have on each device. Streaming services protect their streams and don’t let other websites control or read their players, so they can’t be synced from here; most of them offer their own group-watch features instead.

### Why is one device’s sound late even though the picture is in step?

Its sound goes through something that adds delay after the browser, usually Bluetooth headphones, a speaker or a TV’s sound processing. Set that device’s **Output delay** until the sound lines up, or [measure the delay](https://sync.video/audio-delay-test) and enter it, then press **Remember this delay on this device**.

### What happens if a device loses its connection?

Everyone else carries on. The device that dropped out reconnects to the room by itself when it can, or you can rejoin with the same code after a reload, and it catches up with the others as soon as it hears the host again.

### Does it work on smart TVs?

It depends on the TV’s browser. It needs to open a file from a USB stick or the TV’s storage and play it smoothly, which many built-in browsers can’t do. A laptop, tablet or small computer plugged into the TV by HDMI is the dependable route.

## Other ways to sync

* [ Host a watch party with your own files Friends in different homes, one film, the same moment on every screen. ](https://sync.video/watch-party)
* [ Make a video wall from phones, tablets or TVs One picture split over a grid of screens, with gaps for bezels and every tile in step. ](https://sync.video/video-wall)
* [ Run a silent disco on guests’ phones Headphones on, one room code, and the same beat in every ear without renting a kit. ](https://sync.video/silent-disco)
* [ Compare Syncplay, Jellyfin SyncPlay and this Local-file group watching without a desktop player, a media server or a library. ](https://sync.video/syncplay-alternative)
* [ Host a movie night on Discord Go Live, Watch Together, or a full-quality copy on every screen with Discord for voice. ](https://sync.video/discord-watch-party)
* [ Sync audio and video online Drop one video to fix its delay, or several files to line them up by their sound. ](https://sync.video/)