0xFFFFFFFF when using SetDataSource in Xamarin

I am getting this error using FFmpegMediaMetadataRetriever setDataSource

I want to download a remote file and use the code

string myTempFileName = Path.GetTempFileName();
SambaSubsystem.Instance.CopySambaFileToTempFileName(playListTrack.FileName, myTempFileName);
var myMediaMetadataRetriever = new FFmpegMediaMetadataRetriever();
myMediaMetadataRetriever.SetDataSource(myTempFileName);

I am guessing it is where I am creating the file which is "/data/user/0/com.companyname/cache/tmp577b4c2b.tmp"

I have set the permissions, checked the file exists and tried prefixing with file:// but I think it is where I am creating the file.

Thanks,