修改帧率

//修改fps
-(void) updateFps:(NSInteger) fps{
    NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    
    for (AVCaptureDevice *vDevice in videoDevices) {
        float maxRate = [(AVFrameRateRange *)[vDevice.activeFormat.videoSupportedFrameRateRanges objectAtIndex:0] maxFrameRate];
        if (maxRate >= fps) {
            if ([vDevice lockForConfiguration:NULL]) {
                vDevice.activeVideoMinFrameDuration = CMTimeMake(10, (int)(fps * 10));
                vDevice.activeVideoMaxFrameDuration = vDevice.activeVideoMinFrameDuration;
                [vDevice unlockForConfiguration];
            }
        }
    }
}