Capturing Video with Swift using AVCaptureVideoDataOutput or AVCaptureMovieFileOutput

Question

I need some guidance on how to capture video without having to use an UIImagePicker. The video needs to start and stop on a button click and then this data be saved to the NSDocumentDirectory. I am new to swift so any help will be useful.

The section of code that I need help with is starting and stopping a video session and turning that to data. I created a picture taking version that runs captureStillImageAsynchronouslyFromConnection and saves this data to the NSDocumentDirectory. I have set up a video capturing session and have the code ready to save data but do not know how to get the data from the session.

var previewLayer : AVCaptureVideoPreviewLayer?
var captureDevice : AVCaptureDevice?
var videoCaptureOutput = AVCaptureVideoDataOutput()

let captureSession = AVCaptureSession()

override func viewDidLoad() {
    super.viewDidLoad()

    captureSession.sessionPreset = AVCaptureSessionPreset640x480
    let devices = AVCaptureDevice.devices()

    for device in devices {
        if (device.hasMediaType(AVMediaTypeVideo)) {
            if device.position == AVCaptureDevicePosition.Back {
                captureDevice = device as? AVCaptureDevice
                if captureDevice != nil {
                    beginSession()
                }
            }   
        }
    }
}

func beginSession() {
    var err : NSError? = nil
    captureSession.addInput(AVCaptureDeviceInput(device: captureDevice, error: &err))

    if err != nil {
        println("Error: \(err?.localizedDescription)")
    }

    videoCaptureOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey:kCVPixelFormatType_32BGRA]
    videoCaptureOutput.alwaysDiscardsLateVideoFrames = true

    captureSession.addOutput(videoCaptureOutput)

    previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
    self.view.layer.addSublayer(previewLayer)
    previewLayer?.frame = CGRectMake(0, 0, screenWidth, screenHeight)
    captureSession.startRunning()

    var startVideoBtn = UIButton(frame: CGRectMake(0, screenHeight/2, screenWidth, screenHeight/2))
        startVideoBtn.addTarget(self, action: "startVideo", forControlEvents: UIControlEvents.TouchUpInside)
        self.view.addSubview(startVideoBtn)

    var stopVideoBtn = UIButton(frame: CGRectMake(0, 0, screenWidth, screenHeight/2))
        stopVideoBtn.addTarget(self, action: "stopVideo", forControlEvents: UIControlEvents.TouchUpInside)
        self.view.addSubview(stopVideoBtn)
}

I can supply more code or explanation if needed.

Answer 1

For best results, read the Still and Video Media Capture section from the AV Foundation Programming Guide.

To process frames from AVCaptureVideoDataOutput, you will need a delegate that adopts the AVCaptureVideoDataOutputSampleBufferDelegate protocol. The delegate's captureOutput method will be called whenever a new frame is written. When you set the output’s delegate, you must also provide a queue on which callbacks should be invoked. It will look something like this:

let cameraQueue = dispatch_queue_create("cameraQueue", DISPATCH_QUEUE_SERIAL)
videoCaptureOutput.setSampleBufferDelegate(myDelegate, queue: cameraQueue)
captureSession.addOutput(videoCaptureOutput)

NB: If you just want to save the movie to a file, you may prefer the AVCaptureMovieFileOutput class instead of AVCaptureVideoDataOutput. In that case, you won't need a queue. But you'll still need a delegate, this time adopting the AVCaptureFileOutputRecordingDelegate protocol instead. (The relevant method is still called captureOutput.)

Here's one excerpt from the part about AVCaptureMovieFileOutput from the guide linked to above:

Starting a Recording

You start recording a QuickTime movie using startRecordingToOutputFileURL:recordingDelegate:. You need to supply a file-based URL and a delegate. The URL must not identify an existing file, because the movie file output does not overwrite existing resources. You must also have permission to write to the specified location. The delegate must conform to the AVCaptureFileOutputRecordingDelegate protocol, and must implement the captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error: method.

AVCaptureMovieFileOutput *aMovieFileOutput = <#Get a movie file output#>;
NSURL *fileURL = <#A file URL that identifies the output location#>;
[aMovieFileOutput startRecordingToOutputFileURL:fileURL recordingDelegate:<#The delegate#>];

In the implementation of captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error:, the delegate might write the resulting movie to the Camera Roll album. It should also check for any errors that might have occurred.