Version: 6.4.2

Sync playback across multiple devices

Sync API enables multiple devices to communicate and coordinate their behavior with each other. The communication is facilitated by the server. At any given moment, one of the devices is chosen by the server to be the master and all other devices become slaves.

Uses:

Play content in sync on multiple devices
Videowall - gapless video playback still available

All methods

Methods/Events	Description	Supported since
`connect()`	Connect to the sync server.	1.0.32
`close()`	Closes the connection to the sync server.	1.0.32
`init()`	Join sync group (DEPRECATED)	1.0.32
`joinGroup()`	Join sync group	5.7.0
`wait()`	Wait for other devices in the network for proper sync	1.0.32
`cancelWait()`	Cancel pending waits	5.12.0
`setValue()`	Broadcast values for all master devices (DEPRECATED)	2.0.0
`broadcastValue()`	Used for broadcast values for all master devices	5.7.0
`onValue()`	Event called when device receives value broadcasted by another device in the network	2.0.0
`onStatus()`	Event called when device is connected and periodic every 30s from sync server - report connected devices	2.1.0
`onClosed()`	Event called when synchronizer is closed	5.12.0

GitHub Example

connect()

Connect to the sync server. This initializes the connection and is mandatory to call, since synchronization is an optional feature and doesn’t get initialized by default to save resources and bandwidth. You can optionally specify a custom sync server URI in case you are running the sync server in a custom location.

Parameters

Param	Type	Required	Description
`engine`	String	No	Synchronization engine to use
`uri`	String	No	Address of sync server. Only relevant for `sync-server`. If omitted, the default server will be used.

Engine

Engine	Description
`sync-server`	(Default) Use external sync server. Device will connect to the server via websocket.
`p2p-local`	Synchronize directly with other devices in the local network via UDP and TCP.
`udp`	(Deprecated - use p2p-local) Synchronize directly with other devices in the local network via UDP.

info

All devices, that should be synchronized together, must select the same engine. Otherwise they won't be able to communicate with each other.

Javascript example

// use default engine
await sos.sync.connect().then(() => {
    // do other things once connected
});

// use sync-server engine and default server
await sos.sync.connect({ engine: 'sync-server' }).then(() => {
    // do other things once connected
});

// use sync-server engine and custom server
await sos.sync.connect({
    engine: 'sync-server',
    uri: syncServerUri,
}).then(() => {
    // do other things once connected
});

// use sync-server engine and custom server
await sos.sync.connect({
    engine: 'sync-server',
    uri: syncServerUri,
}).then(() => {
    // do other things once connected
});

// use p2p-local engine
await sos.sync.connect({ engine: 'p2p-local' }).then(() => {
    // do other things once connected
});

// call with syncServerUri as direct argument, now deprecated
// this way it will automatically pick sync-server engine
await sos.sync.connect(syncServerUri).then(() => {
	// do other things once connected
});

close()

Closes the connection to the sync server. Recommended to call this method after the synchronization is not required any longer.

Javascript example

await sos.sync.close().then(() => {
	// do other things once closed
})

init()

warning

This method is deprecated and will be removed in the future. Use joinGroup() instead. These two methods function identically.

Once the user is connected to the server, the initialization of the sync group is required. Before any communication takes place, all participating devices have to be connected and recognize one another. Recommended to call this method early.

Parameters

Param	Type	Required	Description
`groupName`	String	No	By default, all devices will be synced together. To create Groups of devices, independent from each other, specify group name
`deviceIdentification`	String	No	Is identification of device connected to groupName.

Javascript example

await sos.sync.init('someRandomNameGroup', 'device1');

joinGroup()

Once we're connected, we have to join a sync group. Before any communication takes place, all participating devices have to be connected and recognize one another. Recommended to call this method early.

Parameters

Param	Type	Required	Description
`groupName`	String	No	By default, all devices will be synced together. To create Groups of devices, independent from each other, specify group name
`deviceIdentification`	String	No	Is identification of device connected to groupName.

Javascript example

await sos.sync.joinGroup({
    groupName: 'someRandomNameGroup',
    deviceIdentification: 'device1',
});

wait()

One way to synchronize devices is to make them wait for each other at a certain moment. This would be most commonly used before the device hits “play” on a video, to make it wait for other devices so they all start playing the video at the same time.

This method returns a promise that resolves once all the devices meet and are ready to continue together. Any action that results in visible synchronized behavior should be triggered immediately after and any related background preparations should be called before to prevent delays.

Sometimes devices might go out of sync due to unpredictable conditions like loss of internet connection. To ensure re-sync of an out of sync device, you can pass some data as the first argument. This can be any data that informs the whole group about what content is about to play next. Once all devices are ready, data from the master device is passed to everyone and the rest of the data is ignored. Therefore, when implementing your applet you should rely on the result data and not the data that is passed to the wait method as an argument.

Parameters

Param	Type	Required	Description
`data`	Any	No	Information about what content is about to play so all the devices display the same content.
`groupName`	String	No	If `joinGroup` is called with custom group name, the same group name as the second argument has to be passed.
`timeout`	Number	No	Wait timeout on other devices

Returns

Promise that resolves to data picked from the first argument of the master device

cancelWait()

Sometimes it's necessary to cancel a pending wait. One such situation would be when the group has to make a sudden change in content or another behavior but there's a risk that part of the group already called wait() and is waiting for the rest but the rest will never call it at this point. In order to gracefully cleanup any pending activity, use this method.

Any pending wait will be canceled and the promise will be rejected with an error.

Parameters

Param	Type	Required	Description
`groupName`	String	No	If `joinGroup` is called with custom group name, the same group name as the second argument has to be passed.

Javascript example

sos.sync.wait('someData', 'someRandomNameGroup').catch((err) => {
    // this will happend once cancelWait is called
    console.error('wait failed', err);
});

// this will cause above wait promise to reject
await sos.sync.cancelWait('someRandomNameGroup');

Option Broadcast values:

Another way to synchronize devices is to broadcast some values within the group so, in turn, all devices can react to it. Unlike option wait, this is more useful in use cases when the synchronization is based around the content itself, rather than timing.

All Methods

Method	Type	Description	Supported since
`setValue()`	method	Used for broadcast values for all master devices	2.0.0
`onValue()`	event	Event called when device receive any value	2.0.0
`onStatus()`	event	Event called when device is connected and periodic every 30s from sync server - report connected devices	2.1.0

setValue()

warning

This method is deprecated and will be removed in the future. Use broadcastValue() instead. These two methods function identically.

This method can be called by any device to broadcast a value to the whole group.

Parameters

Param	Type	Required	Description
`key`	String	Yes	Values are recognized based their key so different types of values can be broadcasted independently within the group
`value`	Any	Yes	The value to be broadcasted
`groupName`	String	No	If `joinGroup` is called with custom group name, the same group name has to be passed as the third argument

Javascript example

await sos.sync.setValue('some-key', 'some-value', 'some-group');

broadcastValue()

This method can be called by any device to broadcast a value to the whole group.

Parameters

Param	Type	Required	Description
`key`	String	Yes	Values are recognized based their key so different types of values can be broadcasted independently within the group
`value`	Any	Yes	The value to be broadcasted
`groupName`	String	No	If `joinGroup` is called with custom group name, the same group name has to be passed as the third argument

Javascript example

await sos.sync.broadcastValue({
    key: 'some-key',
    value: 'some-value',
    groupName: 'some-group'
});

Event onValue()

Every device should register a listener to receive and process broadcasted values.

Javascript example

await sos.sync.onValue((key, value, groupName) => {
	// do something with the new value
});

Event onStatus()

Is used for receiving information about connected device to sync server. Emitted every 30s, or when device connect or disconnect from server.

Javascript example

await sos.sync.onStatus((connectedPeers) => {
	// do something with the new value
});

info

Since you never know which device is the master at the moment, you should always rely only on the values received by the listener, not the values that the particular device itself is broadcasting.

Event onClosed()

Emitted when synchronizer is closed for whatever reason.

If it closed because close() was called, it will emit without any arguments. if it closed because of an error, it will emit with an error object as the first argument.

Javascript example

await sos.sync.onClosed((error) => {
	if (error) {
        console.error('Synchronizer closed with an error', error);
    } else {
        console.info('Synchronizer closed');
    }
});

Usage with Typescript

You can also use all these methods with signageOS TypeScript.

connect(syncServerUri?: string): Promise<void>;
close(): Promise<void>;
/** @deprecated use joinGroup */
init(groupName?: string, deviceIdentification?: string): Promise<void>;
joinGroup(args: {
    groupName?: string;
    deviceIdentification?: string;
}): Promise<void>;
wait(data?: any, groupName?: string): Promise<any>;
cancelWait(groupName?: string): Promise<void>;
/** @deprecated use broadcastValue */
setValue(key: string, value: any, groupName?: string): Promise<void>;
broadcastValue(args: {
    groupName?: string;
    key: string;
    value: any;
}): Promise<void>;

onValue(listener: (
	key: string, 
	value: any,
	groupName?: string
) => void): void;

onStatus(listener: (
	connectedPeers: string[], 
	groupName?: string
) => void): void;
onClosed(listener: (
	error?: Error;
) => void): void;

Errors

Although we are doing our best, following errors may occur when working with the synchronizer.

Code	Type	Message
51101	InternalSynchronizerError	Synchronizer couldn't connect to the server.
51102	InternalSynchronizerError	The connection wasn't closed correctly.
51103	InternalSynchronizerError	The group initialization failed.
51104	InternalSynchronizerError	Wait failed for unexpected reason.
51105	InternalSynchronizerError	Synchronizer couldn't set the value.

Sync playback across multiple devices

All methods​

connect()​

Parameters​

Engine​

Javascript example​

close()​

Javascript example​

init()​

Parameters​

Javascript example​

joinGroup()​

Parameters​

Javascript example​

wait()​

Parameters​

Returns​

cancelWait()​

Parameters​

Javascript example​

Option Broadcast values:​

All Methods​

setValue()​

Parameters​

Javascript example​

broadcastValue()​

Parameters​

Javascript example​

Event onValue()​

Javascript example​

Event onStatus()​

Javascript example​

Event onClosed()​

Javascript example​

Usage with Typescript​

Errors​

All methods

connect()

Parameters

Engine

Javascript example

close()

Javascript example

init()

Parameters

Javascript example

joinGroup()

Parameters

Javascript example

wait()

Parameters

Returns

cancelWait()

Parameters

Javascript example

Option Broadcast values:

All Methods

setValue()

Parameters

Javascript example

broadcastValue()

Parameters

Javascript example

Event onValue()

Javascript example

Event onStatus()

Javascript example

Event onClosed()

Javascript example

Usage with Typescript

Errors