# Listen for video events

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The Video SDK for iOS fires several video-related callbacks through `ZoomVideoSDKDelegate`. Conform to the delegate and implement the callbacks below to react to video state changes in your session.

If you haven't already set up a delegate, see [Integrate](/docs/video-sdk/ios/integrate/) for details.

## User video status

`onUserVideoStatusChanged` fires when any user starts or stops their video. Use this callback to update your UI. For example, swap a "video off" placeholder for the rendered video, or vice versa.

```swift
func onUserVideoStatusChanged(_ helper: ZoomVideoSDKVideoHelper?, user userArray: [ZoomVideoSDKUser]?) {
    userArray?.forEach { user in
        let isOn = user.getVideoCanvas()?.videoStatus()?.on
        // update the rendered tile or placeholder for this user
    }
}
```

```objectivec
- (void)onUserVideoStatusChanged:(ZoomVideoSDKVideoHelper *)helper user:(NSArray<ZoomVideoSDKUser *> *)userArray {
    for (ZoomVideoSDKUser *user in userArray) {
        BOOL isOn = [[user videoCanvas] videoStatus].on;
        // update the rendered tile or placeholder for this user
    }
}
```

## Spotlight list changes

`onSpotlightVideoChanged` fires whenever the spotlighted user list changes, either because a user was added to or removed from the spotlight. Use this to re-render your gallery layout (for example, to enlarge the spotlighted user's tile).

```swift
func onSpotlightVideoChanged(_ videoHelper: ZoomVideoSDKVideoHelper?, userList: [ZoomVideoSDKUser]?) {
    // userList contains the current spotlighted users
    // re-render your gallery to reflect the new spotlight state
}
```

```objectivec
- (void)onSpotlightVideoChanged:(ZoomVideoSDKVideoHelper *)videoHelper userList:(NSArray<ZoomVideoSDKUser *> *)userList {
    // userList contains the current spotlighted users
    // re-render your gallery to reflect the new spotlight state
}
```

For more on how to add and remove users from the spotlight, see [Spotlight a user](/docs/video-sdk/ios/video/spotlight/).

## Multi-camera stream status

`onMultiCameraStreamStatusChanged` fires when a user enables, disables, mutes, or unmutes a multi-camera stream. The delegate exposes two overloads, one for the raw-data-pipe approach and one for the canvas approach.

```swift
func onMultiCameraStreamStatusChanged(_ status: ZoomVideoSDKMultiCameraStreamStatus, parentUser user: ZoomVideoSDKUser?, videoPipe: ZoomVideoSDKRawDataPipe?) {
    // Raw data pipe variant — see the multi-camera and raw-data docs
}

func onMultiCameraStreamStatusChanged(_ status: ZoomVideoSDKMultiCameraStreamStatus, parentUser user: ZoomVideoSDKUser?, videoCanvas: ZoomVideoSDKVideoCanvas?) {
    // Canvas variant — subscribe a UIView to the canvas to render
}
```

```objectivec
- (void)onMultiCameraStreamStatusChanged:(ZoomVideoSDKMultiCameraStreamStatus)status parentUser:(ZoomVideoSDKUser *)user videoPipe:(ZoomVideoSDKRawDataPipe *)videoPipe {
    // Raw data pipe variant — see the multi-camera and raw-data docs
}

- (void)onMultiCameraStreamStatusChanged:(ZoomVideoSDKMultiCameraStreamStatus)status parentUser:(ZoomVideoSDKUser *)user videoCanvas:(ZoomVideoSDKVideoCanvas *)videoCanvas {
    // Canvas variant — subscribe a UIView to the canvas to render
}
```

For more on how to enable, disable, mute, and unmute multi-camera streams, see [Multiple camera support](/docs/video-sdk/ios/video/multiple-cameras/).

## Alpha channel mode

`onVideoAlphaChannelStatusChanged` fires when alpha channel mode (transparent-background video) is toggled on or off.

```swift
func onVideoAlphaChannelStatusChanged(_ isAlphaChannelOn: Bool) {
    // Adjust rendering to handle transparency
}
```

```objectivec
- (void)onVideoAlphaChannelStatusChanged:(BOOL)isAlphaChannelOn {
    // Adjust rendering to handle transparency
}
```

## Video canvas subscription failure

`onVideoCanvasSubscribeFail` fires when a call to subscribe a `UIView` to a user's video canvas fails. The reason is returned as a `ZoomVideoSDKSubscribeFailReason`. Common failure cases include exceeding the device's render limit or attempting to subscribe before the SDK has finished initializing.

```swift
func onVideoCanvasSubscribeFail(_ failReason: ZoomVideoSDKSubscribeFailReason, user: ZoomVideoSDKUser?, view: UIView?) {
    // Surface an error in your UI, or retry after the underlying issue is resolved
}
```

```objectivec
- (void)onVideoCanvasSubscribeFail:(ZoomVideoSDKSubscribeFailReason)failReason user:(ZoomVideoSDKUser *)user view:(UIView *)view {
    // Surface an error in your UI, or retry after the underlying issue is resolved
}
```

## Camera control requests

`onCameraControlRequestResult` fires on the requesting user's side when a remote camera control request is granted or denied. For the full flow, see [Remote camera control](/docs/video-sdk/ios/video/remote-camera-control/).

```swift
func onCameraControlRequestResult(_ user: ZoomVideoSDKUser?, approved isApproved: Bool) {
    // Update the UI based on whether the request was approved
}
```

```objectivec
- (void)onCameraControlRequestResult:(ZoomVideoSDKUser *)user approved:(BOOL)isApproved {
    // Update the UI based on whether the request was approved
}
```

## Canvas snapshots

`onCanvasSnapshotTaken` fires when a snapshot of a video canvas is successfully captured. `onCanvasSnapshotIncompatible` fires when a snapshot fails because the target user's stream is not compatible with snapshots.

```swift
func onCanvasSnapshotTaken(_ user: ZoomVideoSDKUser, isShare: Bool) {
    // The snapshot is ready — handle it in your UI
}

func onCanvasSnapshotIncompatible(_ user: ZoomVideoSDKUser) {
    // Snapshot was not possible — fall back gracefully
}
```

```objectivec
- (void)onCanvasSnapshotTaken:(ZoomVideoSDKUser *)user isShare:(BOOL)isShare {
    // The snapshot is ready — handle it in your UI
}

- (void)onCanvasSnapshotIncompatible:(ZoomVideoSDKUser *)user {
    // Snapshot was not possible — fall back gracefully
}
```

## Network status

For per-user video network quality changes, implement `onUserNetworkStatusChanged` and check for the video-specific data type, or use `onUserOverallNetworkStatusChanged` for the user's overall quality across all data types.

> **Note**
>
> The dedicated `onUserVideoNetworkStatusChanged` callback is deprecated in favor of the more general `onUserNetworkStatusChanged` and `onUserOverallNetworkStatusChanged` callbacks.

```swift
func onUserNetworkStatusChanged(_ type: ZoomVideoSDKDataType, level: ZoomVideoSDKNetworkStatus, user: ZoomVideoSDKUser?) {
    // React to network quality for a specific data type (such as video)
}

func onUserOverallNetworkStatusChanged(_ level: ZoomVideoSDKNetworkStatus, user: ZoomVideoSDKUser?) {
    // React to the user's overall network quality
}
```

```objectivec
- (void)onUserNetworkStatusChanged:(ZoomVideoSDKDataType)type level:(ZoomVideoSDKNetworkStatus)level user:(ZoomVideoSDKUser *)user {
    // React to network quality for a specific data type (such as video)
}

- (void)onUserOverallNetworkStatusChanged:(ZoomVideoSDKNetworkStatus)level user:(ZoomVideoSDKUser *)user {
    // React to the user's overall network quality
}
```