this method sets the camera frame rate to the max available for the device

iOS Camera - Highest Framerate

- (void)configureCameraForHighestFrameRate:(AVCaptureDevice *)device
{
    AVCaptureDeviceFormat *bestFormat = nil;
    AVFrameRateRange *bestFrameRateRange = nil;
    for ( AVCaptureDeviceFormat *format in [device formats] ) {
        for ( AVFrameRateRange *range in format.videoSupportedFrameRateRanges ) {
            if ( range.maxFrameRate > bestFrameRateRange.maxFrameRate ) {
                bestFormat = format;
                bestFrameRateRange = range;
            }
        }
    }
    if ( bestFormat ) {
        if ( [device lockForConfiguration:NULL] == YES ) {
            device.activeFormat = bestFormat;
            device.activeVideoMinFrameDuration = bestFrameRateRange.minFrameDuration;
            device.activeVideoMaxFrameDuration = bestFrameRateRange.minFrameDuration;
            [device unlockForConfiguration];
        }
    }
}