AVAssetWriter & AVTimedMetadataGroup in AVMultiCamPiP

I'm trying to add metadata every second during video capture in the Swift sample App "AVMultiCamPiP". A simple string that changes every second with a write function triggered by a Timer. Can't get it to work, no matter how I arrange it, always ends up with the error "Cannot create a new metadata adaptor with an asset writer input that has already started writing".

This is the setup section:

		        
 // Add a metadata input

let assetWriterMetaDataInput = AVAssetWriterInput(mediaType: .metadata, outputSettings: nil, sourceFormatHint: AVTimedMetadataGroup().copyFormatDescription())

assetWriterMetaDataInput.expectsMediaDataInRealTime = true

assetWriter.add(assetWriterMetaDataInput)

self.assetWriterMetaDataInput = assetWriterMetaDataInput

This is the timed metadata creation which gets triggered every second:

let newNoteMetadataItem = AVMutableMetadataItem()
newNoteMetadataItem.value = "Some string"  as (NSCopying & NSObjectProtocol)?

let metadataItemGroup = AVTimedMetadataGroup.init(items: [newNoteMetadataItem], timeRange: CMTimeRangeMake( start: CMClockGetTime( CMClockGetHostTimeClock() ), duration: CMTime.invalid ))

movieRecorder?.recordMetaData(meta: metadataItemGroup)

This function is supposed to add the metadata to the track:

    func recordMetaData(meta: AVTimedMetadataGroup) {
        guard isRecording,
            let assetWriter = assetWriter,
            assetWriter.status == .writing,
            let input = assetWriterMetaDataInput,
            input.isReadyForMoreMediaData else {
                return
        }

        let metadataAdaptor = AVAssetWriterInputMetadataAdaptor(assetWriterInput: input)
        metadataAdaptor.append(meta)

    }

I have an older code example in objc which works OK, but it uses "AVCaptureMetadataInput appendTimedMetadataGroup" and writes to an identifier called "quickTimeMetadataLocationNote". I'd like to do something similar in the above Swift code ...

All suggestions are appreciated !