Saving video at 120/240fps

问题

I'm making an app to record videos at the device maximum frame rate (i.e., 120fps in the iPhone 5s and 240 in the 6 and 6s). I've managed to configure the AVCaptureDevice to set the maxFrameRateDuration, I print to the logs the currentDevice.activeFormat.videoSupportedFrameRateRanges and everything works great.

But when I attempt to save the video, it does save it, but at normal frame rate, not at 120 or 240fps.

Please, can anyone help me with this? Any help would be much appreciated.

Thanks in advance.

P.S.: Here is my full code so far

import UIKit
import AVFoundation
import AVKit
import AssetsLibrary

class ViewController: UIViewController, AVCaptureFileOutputRecordingDelegate {

    @IBOutlet weak var cameraButton:UIButton!

    let captureSession = AVCaptureSession()
    var currentDevice:AVCaptureDevice?
    var videoFileOutput:AVCaptureMovieFileOutput?
    var cameraPreviewLayer:AVCaptureVideoPreviewLayer?
    var outputPath: String = ""
    var backgroundRecordId: UIBackgroundTaskIdentifier = UIBackgroundTaskInvalid

    var isRecording = false

    override func viewDidLoad() {
        super.viewDidLoad()

        // Preset the session for taking photo in full resolution
        captureSession.sessionPreset = AVCaptureSessionPresetHigh

        // Get the available devices that is capable of taking video
        let devices = AVCaptureDevice.devicesWithMediaType(AVMediaTypeVideo) as! [AVCaptureDevice]

        // Get the back-facing camera for taking videos
        for device in devices {
            if device.position == AVCaptureDevicePosition.Back {
            currentDevice = device
                configureDevice()
            }
        }

        let captureDeviceInput:AVCaptureDeviceInput
        do {
            captureDeviceInput = try AVCaptureDeviceInput(device: currentDevice)
        } catch {
            print(error)
            return
        }

        // Configure the session with the output for capturing video
        videoFileOutput = AVCaptureMovieFileOutput()

        // Configure the session with the input and the output devices
        captureSession.addInput(captureDeviceInput)
        captureSession.addOutput(videoFileOutput)

        // Provide a camera preview
        cameraPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        view.layer.addSublayer(cameraPreviewLayer!)
        cameraPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
        cameraPreviewLayer?.frame = view.layer.frame

        // Bring the camera button to front
        view.bringSubviewToFront(cameraButton)
        captureSession.startRunning()    
    }

    func configureDevice() {

        var bestFormat: AVCaptureDeviceFormat? = nil
        var bestFrameRateRange: AVFrameRateRange? = nil
        var bestPixelArea: Int32 = 0
        for format in currentDevice!.formats {
            let dims: CMVideoDimensions = CMVideoFormatDescriptionGetDimensions(format.formatDescription)
            let pixelArea: Int32 = dims.width * dims.height
            let ranges = format.videoSupportedFrameRateRanges as! [AVFrameRateRange];
            for range in ranges {
                //print ("[",dims.width,",",dims.width,"] : ",range.maxFrameRate);
                if bestFrameRateRange==nil || range.maxFrameRate > bestFrameRateRange!.maxFrameRate || ((range.maxFrameRate == bestFrameRateRange!.maxFrameRate) && (pixelArea > bestPixelArea)) {
                    bestFormat = format as? AVCaptureDeviceFormat
                    bestFrameRateRange = range
                    bestPixelArea = pixelArea
                }
            }
        }            

        do {

            try currentDevice!.lockForConfiguration() {

            currentDevice!.activeFormat = bestFormat
            currentDevice!.activeVideoMinFrameDuration = bestFrameRateRange!.minFrameDuration
            currentDevice!.activeVideoMaxFrameDuration = bestFrameRateRange!.minFrameDuration              

        }
        catch{}         

        print(currentDevice!.activeFormat.videoSupportedFrameRateRanges)

        currentDevice!.unlockForConfiguration()            
    }    


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    // MARK: - AVCaptureFileOutputRecordingDelegate methods

    func captureOutput(captureOutput: AVCaptureFileOutput!, didFinishRecordingToOutputFileAtURL outputFileURL: NSURL!, fromConnections connections: [AnyObject]!, error: NSError!) {


        if error != nil {
            print(error)
            return
        }

        let backgroundRecordId: UIBackgroundTaskIdentifier = self.backgroundRecordId
        self.backgroundRecordId = UIBackgroundTaskInvalid

        ALAssetsLibrary().writeVideoAtPathToSavedPhotosAlbum(outputFileURL, completionBlock: {
            (assetURL:NSURL!, error:NSError!) in
            if error != nil{
                print(error)

            }

            do {
                try NSFileManager.defaultManager().removeItemAtURL(outputFileURL)
            } catch _ {
            }

            if backgroundRecordId != UIBackgroundTaskInvalid {
                UIApplication.sharedApplication().endBackgroundTask(backgroundRecordId)
            }

        })
        performSegueWithIdentifier("playVideo", sender: outputFileURL)
    }

    // MARK: - Segue methods

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "playVideo" {
            let videoPlayerViewController = segue.destinationViewController as! AVPlayerViewController
            let videoFileURL = sender as! NSURL
            videoPlayerViewController.player = AVPlayer(URL: videoFileURL)

        }
    }


    // MARK: - Action methods

    @IBAction func unwindToCamera(segue:UIStoryboardSegue) {

    }

    @IBAction func capture(sender: AnyObject) {
        if !isRecording {
            isRecording = true

            UIView.animateWithDuration(0.5, delay: 0.0, options: [.Repeat, .Autoreverse, .AllowUserInteraction], animations: { () -> Void in
                self.cameraButton.transform = CGAffineTransformMakeScale(0.5, 0.5)
                }, completion: nil)

            let outputPath: String = NSTemporaryDirectory() + "output.mov"
            let outputFileURL = NSURL(fileURLWithPath: outputPath)
            videoFileOutput?.startRecordingToOutputFileURL(outputFileURL, recordingDelegate: self)
        } else {
            isRecording = false

            UIView.animateWithDuration(0.5, delay: 1.0, options: [], animations: { () -> Void in
                self.cameraButton.transform = CGAffineTransformMakeScale(1.0, 1.0)
                }, completion: nil)
            cameraButton.layer.removeAllAnimations()

            videoFileOutput?.stopRecording()

        }
    }        
}

回答1:

You're calling configDevice() too early and your configuration is being replaced.

Call configDevice() after you've added the capture device's input:

// Configure the session with the input and the output devices
captureSession.addInput(captureDeviceInput)
configureDevice()

回答2:

Your question is pretty old, but still I want to add something. I think you have to set both to the maxFrameDuration. Give this one a try:

   currentDevice!.activeVideoMinFrameDuration = bestFrameRateRange!.maxFrameDuration
   currentDevice!.activeVideoMaxFrameDuration = bestFrameRateRange!.maxFrameDuration              

来源：https://stackoverflow.com/questions/33753843/saving-video-at-120-240fps