AVCapture在iOS 7中以60 fps捕获和获取帧缓冲

Question

I'm developping an app which requires capturing framebuffer at as much fps as possible. I've already figured out how to force iphone to capture at 60 fps but

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection

method is being called only 15 times a second, which means that iPhone downgrades capture output to 15 fps.

Has anybody faced such problem? Is there any possibility to increase capturing frame rate?

Update my code:

camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
if([camera isTorchModeSupported:AVCaptureTorchModeOn]) {
   [camera lockForConfiguration:nil];
   camera.torchMode=AVCaptureTorchModeOn;
   [camera unlockForConfiguration];
}
[self configureCameraForHighestFrameRate:camera];

// Create a AVCaptureInput with the camera device
NSError *error=nil;
AVCaptureInput* cameraInput = [[AVCaptureDeviceInput alloc] initWithDevice:camera error:&error];
if (cameraInput == nil) {
   NSLog(@"Error to create camera capture:%@",error);
}

// Set the output
AVCaptureVideoDataOutput* videoOutput = [[AVCaptureVideoDataOutput alloc] init];

// create a queue to run the capture on
dispatch_queue_t captureQueue=dispatch_queue_create("captureQueue", NULL);

// setup our delegate
[videoOutput setSampleBufferDelegate:self queue:captureQueue];

// configure the pixel format
videoOutput.videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA], (id)kCVPixelBufferPixelFormatTypeKey,
                             nil];

// Add the input and output
[captureSession addInput:cameraInput];
[captureSession addOutput:videoOutput];

I took configureCameraForHighestFrameRate method here https://developer.apple.com/library/mac/documentation/AVFoundation/Reference/AVCaptureDevice_Class/Reference/Reference.html

Answer 1

I am getting samples at 60 fps on the iPhone 5 and 120 fps on the iPhone 5s, both when doing real time motion detection in captureOutput and when saving the frames to a video using AVAssetWriter.

You have to set thew AVCaptureSession to a format that supports 60 fps:

AVsession = [[AVCaptureSession alloc] init];

AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *capInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
if (capInput) [AVsession addInput:capInput];

for(AVCaptureDeviceFormat *vFormat in [videoDevice formats] ) 
{
    CMFormatDescriptionRef description= vFormat.formatDescription;
    float maxrate=((AVFrameRateRange*)[vFormat.videoSupportedFrameRateRanges objectAtIndex:0]).maxFrameRate;

    if(maxrate>59 && CMFormatDescriptionGetMediaSubType(description)==kCVPixelFormatType_420YpCbCr8BiPlanarFullRange)
    {
        if ( YES == [videoDevice lockForConfiguration:NULL] ) 
        {
           videoDevice.activeFormat = vFormat;
           [videoDevice setActiveVideoMinFrameDuration:CMTimeMake(10,600)];
           [videoDevice setActiveVideoMaxFrameDuration:CMTimeMake(10,600)];
           [videoDevice unlockForConfiguration];
           NSLog(@"formats  %@ %@ %@",vFormat.mediaType,vFormat.formatDescription,vFormat.videoSupportedFrameRateRanges);
        }
     }
}

prevLayer = [AVCaptureVideoPreviewLayer layerWithSession: AVsession];
prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[self.view.layer addSublayer: prevLayer];

AVCaptureVideoDataOutput *videoOut = [[AVCaptureVideoDataOutput alloc] init];
dispatch_queue_t videoQueue = dispatch_queue_create("videoQueue", NULL);
[videoOut setSampleBufferDelegate:self queue:videoQueue];

videoOut.videoSettings = @{(id)kCVPixelBufferPixelFormatTypeKey: @(kCVPixelFormatType_32BGRA)};
videoOut.alwaysDiscardsLateVideoFrames=YES;

if (videoOut)
{
    [AVsession addOutput:videoOut];
    videoConnection = [videoOut connectionWithMediaType:AVMediaTypeVideo];
}

Two other comment if you want to write to a file using AVAssetWriter. Don't use the pixelAdaptor, just ad the samples with

[videoWriterInput appendSampleBuffer:sampleBuffer]

Secondly when setting up the assetwriter use

[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
                                   outputSettings:videoSettings 
                                 sourceFormatHint:formatDescription];

The sourceFormatHint makes a difference in writing speed.

Answer 2

I have developed the same function for Swift 2.0. I post here the code for who could need it:

// Set your desired frame rate
func setupCamera(maxFpsDesired: Double = 120) {
var captureSession = AVCaptureSession()
    captureSession.sessionPreset = AVCaptureSessionPreset1920x1080
    let backCamera = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    do{ let input = try AVCaptureDeviceInput(device: backCamera)
        captureSession.addInput(input) }
    catch { print("Error: can't access camera")
        return
    }
    do {
        var finalFormat = AVCaptureDeviceFormat()
        var maxFps: Double = 0
        for vFormat in backCamera!.formats {
            var ranges      = vFormat.videoSupportedFrameRateRanges as!  [AVFrameRateRange]
            let frameRates  = ranges[0]
            /*
                 "frameRates.maxFrameRate >= maxFps" select the video format
                 desired with the highest resolution available, because
                 the camera formats are ordered; else
                 "frameRates.maxFrameRate > maxFps" select the first
                 format available with the desired fps 
            */
            if frameRates.maxFrameRate >= maxFps && frameRates.maxFrameRate <= maxFpsDesired {
                maxFps = frameRates.maxFrameRate
                finalFormat = vFormat as! AVCaptureDeviceFormat
            }
        }
        if maxFps != 0 {
           let timeValue = Int64(1200.0 / maxFps)
           let timeScale: Int64 = 1200
           try backCamera!.lockForConfiguration()
           backCamera!.activeFormat = finalFormat
           backCamera!.activeVideoMinFrameDuration = CMTimeMake(timeValue, timeScale)
           backCamera!.activeVideoMaxFrameDuration = CMTimeMake(timeValue, timeScale)              backCamera!.focusMode = AVCaptureFocusMode.AutoFocus
           backCamera!.unlockForConfiguration()
        }
    }
    catch {
         print("Something was wrong")
    }
    let videoOutput = AVCaptureVideoDataOutput()
    videoOutput.alwaysDiscardsLateVideoFrames = true
    videoOutput.videoSettings = NSDictionary(object: Int(kCVPixelFormatType_32BGRA),
        forKey: kCVPixelBufferPixelFormatTypeKey as String) as [NSObject : AnyObject]
    videoOutput.setSampleBufferDelegate(self, queue: dispatch_queue_create("sample buffer delegate", DISPATCH_QUEUE_SERIAL))
    if captureSession.canAddOutput(videoOutput){
        captureSession.addOutput(videoOutput) }
    let previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
    view.layer.addSublayer(previewLayer)
    previewLayer.transform =  CATransform3DMakeRotation(-1.5708, 0, 0, 1);
    previewLayer.frame = self.view.bounds
    previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    self.view.layer.addSublayer(previewLayer)
    captureSession.startRunning()
}

Answer 3

Had the same problem. Fixed by using this function after [AVCaptureSession addInput:cameraDeviceInput] . Somehow I could not change the framerate on my iPad pro before capture session was started. So at first I changed video format after the device was added to the capture session.

- (void)switchFormatWithDesiredFPS:(CGFloat)desiredFPS
{
    BOOL isRunning = _captureSession.isRunning;

    if (isRunning)  [_captureSession stopRunning];

    AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceFormat *selectedFormat = nil;
    int32_t maxWidth = 0;
    AVFrameRateRange *frameRateRange = nil;

    for (AVCaptureDeviceFormat *format in [videoDevice formats]) {

        for (AVFrameRateRange *range in format.videoSupportedFrameRateRanges) {

            CMFormatDescriptionRef desc = format.formatDescription;
            CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(desc);
            int32_t width = dimensions.width;

            if (range.minFrameRate <= desiredFPS && desiredFPS <= range.maxFrameRate && width >= maxWidth) {

                selectedFormat = format;
                frameRateRange = range;
                maxWidth = width;
            }
        }
    }

    if (selectedFormat) {

        if ([videoDevice lockForConfiguration:nil]) {

            NSLog(@"selected format:%@", selectedFormat);
            videoDevice.activeFormat = selectedFormat;
            videoDevice.activeVideoMinFrameDuration = CMTimeMake(1, (int32_t)desiredFPS);
            videoDevice.activeVideoMaxFrameDuration = CMTimeMake(1, (int32_t)desiredFPS);
            [videoDevice unlockForConfiguration];
        }
    }

    if (isRunning) [_captureSession startRunning];
}