# Core features

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The Video SDK for iOS lets you programmatically control user video during a session: check video status, start video, stop video, and render one or many users. For switching, mirroring, rotating, and other per-device camera operations, see [Camera controls](/docs/video-sdk/ios/video/camera-controls/).

> **Camera permission required.**
>
> Before using video, your app must request camera access. Add an `NSCameraUsageDescription` entry to your `Info.plist` and request permission at runtime. For details, see [Requesting authorization to capture and save media](https://developer.apple.com/documentation/avfoundation/capture_setup/requesting_authorization_to_capture_and_save_media).

## Check whether video is on

To check whether a user has their video on, read `on` from the user's `videoStatus` to get a boolean indicating whether that user's video is on in the session.

```swift
let isVideoOn = user.getVideoCanvas()?.videoStatus()?.on
```

```objectivec
BOOL isVideoOn = [[user videoCanvas] videoStatus].on;
```

## Start video

Start video by calling `startVideo` on the `ZoomVideoSDKVideoHelper`. Be sure your app has camera permission before calling, or the SDK can't capture from the camera.

```swift
if let videoHelper = ZoomVideoSDK.shareInstance()?.getVideoHelper() {
    videoHelper.startVideo()
}
```

```objectivec
ZoomVideoSDKVideoHelper *videoHelper = [[ZoomVideoSDK shareInstance] getVideoHelper];
if (videoHelper) {
    [videoHelper startVideo];
}
```

## Stop video

Stop video by calling `stopVideo` on the `ZoomVideoSDKVideoHelper`.

```swift
ZoomVideoSDK.shareInstance()?.getVideoHelper()?.stopVideo()
```

```objectivec
[[[ZoomVideoSDK shareInstance] getVideoHelper] stopVideo];
```

## Render a user's video

To render a user's video, get the user's `ZoomVideoSDKVideoCanvas` and subscribe a `UIView` to it.

```swift
// Get the user's videoCanvas.
if let usersVideoCanvas = user.getVideoCanvas() {
    // Set the video aspect.
    let videoAspect = ZoomVideoSDKVideoAspect.panAndScan
    // Subscribe the user's videoCanvas to render their video stream.
    usersVideoCanvas.subscribe(with: view, andAspectMode: videoAspect)
}
```

```objectivec
// Get the user's videoCanvas.
ZoomVideoSDKVideoCanvas *usersVideoCanvas = [user getVideoCanvas];
// Set the video aspect.
ZoomVideoSDKVideoAspect videoAspect = ZoomVideoSDKVideoAspect_PanAndScan;
// Subscribe the user's videoCanvas to render their video stream.
[usersVideoCanvas subscribeWithView:view andAspectMode:videoAspect];
```

The `aspect` parameter controls how Zoom fits the video into the view.

| Type                                  | Description                                                                              |
| ------------------------------------- | ---------------------------------------------------------------------------------------- |
| `ZoomVideoSDKVideoAspect_Original`    | Display video without any modifications.                                                 |
| `ZoomVideoSDKVideoAspect_Full_Filled` | Stretch the video to fill the canvas.                                                    |
| `ZoomVideoSDKVideoAspect_LetterBox`   | Add black bars (top/bottom or left/right) so the full frame is visible without cropping. |
| `ZoomVideoSDKVideoAspect_PanAndScan`  | Crop the frame to fill the canvas without bars.                                          |

For more on choosing an aspect mode and on responsive layouts, see [Aspect ratio and orientation](/docs/video-sdk/ios/video/best-practices/#aspect-ratio-and-orientation).

### Remove a user's video from a canvas

When a user leaves the session, or when you want to recycle a view for a different user, unsubscribe from the canvas.

```swift
if let usersVideoCanvas = user.getVideoCanvas() {
    usersVideoCanvas.unSubscribe(with: view)
}
```

```objectivec
ZoomVideoSDKVideoCanvas *usersVideoCanvas = [user getVideoCanvas];
[usersVideoCanvas unSubscribeWithView:view];
```

## Render multiple users

To render multiple users at once (gallery view), iterate over the users in the session and subscribe a `UIView` for each. Respond to `onUserJoin` to add new users as they enter, and `onUserLeave` to unsubscribe.

```swift
func onUserJoin(_ helper: ZoomVideoSDKUserHelper?, users userArray: [ZoomVideoSDKUser]?) {
    userArray?.forEach { user in
        // Create or dequeue a UIView for this user, add it to your gallery container,
        // then subscribe the user's canvas to it.
        user.getVideoCanvas()?.subscribe(with: view, andAspectMode: .original)
    }
}

func onUserLeave(_ helper: ZoomVideoSDKUserHelper?, users userArray: [ZoomVideoSDKUser]?) {
    userArray?.forEach { user in
        // Unsubscribe and remove the corresponding view from the container.
        user.getVideoCanvas()?.unSubscribe(with: view)
    }
}
```

```objectivec
- (void)onUserJoin:(ZoomVideoSDKUserHelper *)helper users:(NSArray<ZoomVideoSDKUser *> *)userArray {
    for (ZoomVideoSDKUser *user in userArray) {
        // Create or dequeue a UIView for this user, add it to your gallery container,
        // then subscribe the user's canvas to it.
        [[user getVideoCanvas] subscribeWithView:view andAspectMode:ZoomVideoSDKVideoAspect_Original];
    }
}

- (void)onUserLeave:(ZoomVideoSDKUserHelper *)helper users:(NSArray<ZoomVideoSDKUser *> *)userArray {
    for (ZoomVideoSDKUser *user in userArray) {
        // Unsubscribe and remove the corresponding view from the container.
        [[user getVideoCanvas] unSubscribeWithView:view];
    }
}
```

For grid layout and density recommendations, see [Layout and density](/docs/video-sdk/ios/video/best-practices/#layout-and-density).