Inconsistent FPS (20 FPS Issue) While Recording Video Using AVCaptureSession.

Hi,

I am recording video using my app. And setting up fps also using below code. But sometime video is being recorded using 20 FPS. Can someone please let me know what I am doing wrong?

private func eightBitVariantOfFormat() -> AVCaptureDevice.Format? {
        let activeFormat = self.videoDeviceInput.device.activeFormat
        let fpsToBeSupported: Int = 60
        debugPrint("fpsToBeSupported - \(fpsToBeSupported)" as AnyObject)
        
        let allSupportedFormats = self.videoDeviceInput.device.formats
        debugPrint("all formats - \(allSupportedFormats)" as AnyObject)
        
        let activeDimensions = CMVideoFormatDescriptionGetDimensions(activeFormat.formatDescription)
        debugPrint("activeDimensions - \(activeDimensions)" as AnyObject)
        
        let filterBasedOnDimensions = allSupportedFormats.filter({ (CMVideoFormatDescriptionGetDimensions($0.formatDescription).width == activeDimensions.width) && (CMVideoFormatDescriptionGetDimensions($0.formatDescription).height == activeDimensions.height) })
        
        if filterBasedOnDimensions.isEmpty {
            // Dimension not found. Required format not found to handle.
            debugPrint("Dimension not found" as AnyObject)
            return activeFormat
        }
        
        debugPrint("filterBasedOnDimensions - \(filterBasedOnDimensions)" as AnyObject)
        
        let filterBasedOnMaxFrameRate = filterBasedOnDimensions.compactMap({ format in
            let videoSupportedFrameRateRanges = format.videoSupportedFrameRateRanges
            if !videoSupportedFrameRateRanges.isEmpty {
                let contains = videoSupportedFrameRateRanges.contains(where: { Int($0.maxFrameRate) >= fpsToBeSupported })
                if contains {
                    return format
                } else {
                    return nil
                }
            } else {
                return nil
            }
        })
        
        debugPrint("allFormatsToBeSupported - \(filterBasedOnMaxFrameRate)" as AnyObject)
        
        guard !filterBasedOnMaxFrameRate.isEmpty else {
            debugPrint("Taking default active format as nothing found when filtered using desired FPS" as AnyObject)
            return activeFormat
        }
        
        var formatToBeUsed: AVCaptureDevice.Format!
        if let four_two_zero_v = filterBasedOnMaxFrameRate.first(where: { CMFormatDescriptionGetMediaSubType($0.formatDescription) == kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange}) {
            // 'vide'/'420v'
            formatToBeUsed = four_two_zero_v
        } else {
            // Take the first one from above array.
            formatToBeUsed = filterBasedOnMaxFrameRate.first
        }
        
        do {
            try self.videoDeviceInput.device.lockForConfiguration()
            self.videoDeviceInput.device.activeFormat = formatToBeUsed
            self.videoDeviceInput.device.activeVideoMinFrameDuration = CMTimeMake(value: 1, timescale: Int32(fpsToBeSupported))
            self.videoDeviceInput.device.activeVideoMaxFrameDuration = CMTimeMake(value: 1, timescale: Int32(fpsToBeSupported))
            if videoDeviceInput.device.isFocusModeSupported(.continuousAutoFocus) {
                self.videoDeviceInput.device.focusMode = AVCaptureDevice.FocusMode.continuousAutoFocus
            }
            self.videoDeviceInput.device.unlockForConfiguration()
        } catch let error {
            debugPrint("\(error)" as AnyObject)
        }
        return formatToBeUsed
    }