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Set custom AVFrameRateRange for AVCaptureSession

I try to take 5 shots every second using AVCaptureSession, and I'm not sure I understand what AVFrameRange means. I currently have code that installs the device:

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

and tries to establish a activeVideoMinFrameDurationand activeVideoMaxFrameDurationthe custom value CMTimeMake(1, 5). Apple says that I can only use one of the AVFrameRanges that they provided.

When I NSLogged them, I get (2, 30), (2.60) and (2.24). First I want to know what that means? Is this the frame rate with which the camera works, or the interval for capturing frames (that is, what I'm trying to do)?

If this is not the case, what can I do to save 5 frames per second on my sampleBufferDelegate method? Currently it gives me every single frame, because the method is called every time there is a frame, so I just need a pointer to how I can capture only 5 per second.

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2 answers

Here is the working code we used that sets the frame rate to 5 per second.

If you measure CaptureOutput calls using this code, you can see that the camera frames are called every 200 ms (i.e. 5 frames per second). (We just tested this for confirmation.)

Change the desired FrameRate to get different camera frame rates.

- (void)attemptToConfigure5FPS
{
    NSError *error;
    if (![self lockForConfiguration:&error]) {
        NSLog(@"Could not lock device %@ for configuration: %@", self, error);
        return;
    }

    AVCaptureDeviceFormat *format = self.activeFormat;
    double epsilon = 0.00000001;

    int desiredFrameRate = 5;

    for (AVFrameRateRange *range in format.videoSupportedFrameRateRanges) {

            if (range.minFrameRate <= (desiredFrameRate + epsilon) &&
            range.maxFrameRate >= (desiredFrameRate - epsilon)) {

            self.activeVideoMaxFrameDuration = (CMTime){
                .value = 1,
                .timescale = desiredFrameRate,
                .flags = kCMTimeFlags_Valid,
                .epoch = 0,
            };
            self.activeVideoMinFrameDuration = (CMTime){
                .value = 1,
                .timescale = desiredFrameRate,
                .flags = kCMTimeFlags_Valid,
                .epoch = 0,
            };           
            break;
        }
    }

    [self unlockForConfiguration];
}
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: Apple RosyWriter, , FPS

- (void)configureCamera:(AVCaptureDevice *)videoDevice withFrameRate:(int)desiredFrameRate
{
    BOOL isFPSSupported = NO;
    AVCaptureDeviceFormat *currentFormat = [videoDevice activeFormat];
    for ( AVFrameRateRange *range in currentFormat.videoSupportedFrameRateRanges ) {
        if ( range.maxFrameRate >= desiredFrameRate && range.minFrameRate <= desiredFrameRate )        {
            isFPSSupported = YES;
            break;
        }
    }

    if( isFPSSupported ) {
        if ( [videoDevice lockForConfiguration:NULL] ) {
            videoDevice.activeVideoMaxFrameDuration = CMTimeMake( 1, desiredFrameRate );
            videoDevice.activeVideoMinFrameDuration = CMTimeMake( 1, desiredFrameRate );
            [videoDevice unlockForConfiguration];
        }
    }
}

(activeFormat) FPS, activeFormat, FPS. , .

- (void)configureCamera:(AVCaptureDevice *)device withFrameRate:(int)desiredFrameRate
{
    AVCaptureDeviceFormat *desiredFormat = nil;
    for ( AVCaptureDeviceFormat *format in [device formats] ) {
        for ( AVFrameRateRange *range in format.videoSupportedFrameRateRanges ) {
            if ( range.maxFrameRate >= desiredFrameRate && range.minFrameRate <= desiredFrameRate ) {
                desiredFormat = format;
                goto desiredFormatFound;
            }
        }
    }

    desiredFormatFound:
    if ( desiredFormat ) {
        if ( [device lockForConfiguration:NULL] == YES ) {
            device.activeFormat = desiredFormat ;
            device.activeVideoMinFrameDuration = CMTimeMake ( 1, desiredFrameRate );
            device.activeVideoMaxFrameDuration = CMTimeMake ( 1, desiredFrameRate );
            [device unlockForConfiguration];
        }
    }
}

. AVCaptureConnection videoMinFrameDuration FPS .

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