# Screen share - iOS 4.x

In this guide we'll show you how to share your iOS screen with other Participants connected to a Room using `ReplayKit.framework`. By using `ReplayKit.framework`, you have the ability to consume `CMSampleBuffer` objects that are produced by ReplayKit and convert them into `VideoFrame` objects that can be shared via a `LocalVideoTrack`.

There are two main ways that this can be accomplished depending on what screen content you wish to share. If you only want to share your application's screens, you can use the In-App Capture method. All of the code required is contained inside your application. If you want to share screens outside of your application, such as the Home Screen or other applications, you can use the Broadcast Extension method. Both methodologies are implemented in our [ReplayKit Example](https://github.com/twilio/video-quickstart-ios/tree/master/ReplayKitExample) application and should be used for reference.

## In-App Capture Method

When you only want to share the screens of your application, you can use the In-App Capturing method. To capture your application's screens, you use the `AppScreenSource` class. `AppScreenSource` conforms to `VideoSource` and uses `ReplayKit.RPScreenRecorder` internally to capture video of your app's screen. To begin recording, you call the `startCapture()` method.

```swift
if let source = AppScreenSource(), let track = LocalVideoTrack(source: source) {
    room.localParticipant?.publishVideoTrack(track)
    source.startCapture()
}
```

When you are done sharing your screen, you can call the `stopCapture()` method of `AppScreenSource` and remove your `LocalVideoTrack` using the methods on your `LocalParticipant` object.

For further guidance on this approach, check out the [ViewController](https://github.com/twilio/video-quickstart-ios/blob/master/ReplayKitExample/ReplayKitExample/ViewController.swift) class in the [ReplayKitExample](https://github.com/twilio/video-quickstart-ios/tree/master/ReplayKitExample) example application.

## Broadcast Extension Method

With ReplayKit, it is possible to not only share your application's screens but also other applications on the device. This configuration requires that you create a ReplayKit broadcast extension that is included with your application. In your ReplayKit broadcast extension, you create a subclass of [`RPBroadcastSampleHandler`](https://developer.apple.com/documentation/replaykit/rpbroadcastsamplehandler). This class will be responsible for handling the samples produced by ReplayKit. The [SampleHandler](https://github.com/twilio/video-quickstart-ios/blob/master/ReplayKitExample/BroadcastExtension/SampleHandler.swift) class in the [ReplayKitExample](https://github.com/twilio/video-quickstart-ios/tree/master/ReplayKitExample) shows an example implementation.

You will need to implement an object that conforms to the `VideoSource` protocol. This object is then provided when you create a `LocalVideoTrack` object. Your `VideoSource` object is responsible for consuming the `CMSampleBuffer` objects provided by ReplayKit and providing `VideoFrame` objects to its `VideoSink`.

The `ReplayKitVideoSource` class in our [example application](https://github.com/twilio/video-quickstart-ios/blob/master/ReplayKitExample/ReplayKitExample/ReplayKitVideoSource.swift) shows an implementation of this. Each time `ReplayKit.framework` produces a `CMSampleBuffer` object, it gets passed in to the `processFrame()` method. The `ReplayKitVideoSource` object handles the work of converting the frame into a `VideoFrame` object and passes it off to the `VideoSink`.

For example, creating a `LocalVideoTrack` to transmit video frames produced by ReplayKit using `ReplayKitVideoSouce` would be as follows.

```swift
var screenTrack: LocalVideoTrack?
var videoSource: ReplayKitVideoSource?

...

videoSource = ReplayKitVideoSource(isScreencast: true,
                                   telecineOptions: ReplayKitVideoSource.TelecineOptions.disabled)

screenTrack = LocalVideoTrack(source: videoSource!,
                              enabled: true,
                              name: "Screen")
```

Once configured, you can share `screenTrack` as you would any other `LocalVideoTrack` in your Room. You can provide it when you join the room via the `videoTracks` `ConnectOption` or adding it later via your `LocalParticipant` object.

To start the ReplayKit broadcast, your application must present the [`RPBroadcastActivityViewController`](https://developer.apple.com/documentation/replaykit/rpbroadcastactivityviewcontroller) which allows the user to select your broadcast extension as the broadcasting service. Once the user starts the broadcast, the `broadcastStarted()` method will be invoked. The `broadcastStarted()` method in the example `SampleHandler` class then creates a `ReplayKitVideoSource` and an associated `LocalVideoTrack`, and connects to a `Room`. Each time ReplayKit generates a video frame, the `processSampleBuffer()` method is invoked and the `sampleBuffer` is provided to the `ReplayKitVideoSource` for handling.

It is important to note that a ReplayKit broadcast extension must operate with limited memory. It is highly recommended that you use Group Rooms and set the `isAutomaticSubscriptionEnabled` `ConnectOptions` property to `false` when connecting to a Room within in the extension.

For further guidance on this approach, check out the [ReplayKitExample](https://github.com/twilio/video-quickstart-ios/tree/master/ReplayKitExample) example application.