Understanding AVFoundation Video Recording Capture Sessions

AVFoundation is a framework in iOS that provides a high-level API for tasks such as audio and video playback, recording, and editing. In this section, we’ll delve into how AVFoundation manages video recording capture sessions.

When you start a video recording session using the startCaptureSession method of an AVCaptureDevice, you’re initiating a process where data is captured from your device’s camera or other sources (like microphones) and stored in a buffer. The recording continues until you manually stop it by calling the `stop() method on the AVCaptureSession.

The AVCaptureSession class manages this session, handling tasks like:

• Buffer management: Storing and retrieving data from buffers
• Queue management: Processing capture requests and callbacks
• Session state management: Tracking changes in the recording status

In addition to these responsibilities, an AVCaptureSession also maintains a connection with the user interface. In our case, we’re interested in how this framework interacts with view controllers.

Managing Session States

When you switch between different views in your app (e.g., from one storyboard view to another), the session state changes accordingly. If the new view is an alternate screen layout (like a flipside or another storyboard view) and the recording was not stopped manually by tapping the stop icon, we need to ensure that the recording stops and saves automatically.

To achieve this, we’ll need to leverage one of iOS’s built-in callback methods: viewWillDisappear.

The viewWillDisappear Method

When an app is moving from a current view to another, iOS provides various opportunities for code execution at different stages. One of these stages is the viewWillDisappear method.

```markdown The - (void)viewWillDisappear:(BOOL) animated method is called immediately before the receiver’s view goes away; this can happen when the app’s user transitions to another screen or window, or when the application terminates.

In our case, we want to stop and tear down the video recording session whenever the current view disappears. So, we’ll place the code for stopping the session in the viewWillDisappear method.

**```markdown**
To prevent the video recording from continuing when switching between views, you can call the `stopAndTearDownCaptureSession` method inside the `viewWillDisappear` method.

Here's an example implementation:
```markdown
## Stopping and Tearing Down the Capture Session on View Disappear

### 1. Importing Necessary Frameworks and Classes
```markdown
#import <AVFoundation/AVFoundation.h>

// Assuming that self.videoProcessor is an instance of AVCaptureVideoPreviewLayer or similar class.

2. Placing Code Inside viewWillDisappear Method

We’ll call the stopAndTearDownCaptureSession method, followed by setting its delegate to nil and clearing its reference.

- (void)viewWillDisappear:(BOOL) animated {
    [super viewWillDisappear:animated];

    // Stop capturing video data.
    [self.videoProcessor stopAndTearDownCaptureSession];
    
    // Set the session's delegate to nil to prevent further processing of capture requests.
    self.videoProcessor.delegate = nil;
    
    // Clear the reference to the video processor object to release any retained resources.
    self.videoProcessor = nil;
}

By placing this code in the viewWillDisappear method, you ensure that your app stops recording and saves the session data as soon as it switches to an alternate view.

Key Takeaways

• To stop a video recording session when switching between views, use the stopAndTearDownCaptureSession method inside the viewWillDisappear method.
• Set the session’s delegate to nil to prevent further processing of capture requests and release any retained resources.
• This approach ensures that your app stops recording and saves the session data as soon as it switches to an alternate view.

Conclusion

Managing video recording sessions in AVFoundation can be complex, especially when dealing with view controller transitions. By understanding how the framework interacts with view controllers and leveraging iOS’s built-in callback methods like viewWillDisappear, you can ensure that your app stops recording and saves the session data effectively.

Last modified on 2025-04-29