Exiv2 maps and will convert Exif tags and IPTC datasets to and from XMP properties.

This function is available via the import/export command line options: exiv2 -eX image.jpg; exiv2 -iX image.jpg
and via the exiv2 API: convert.hpp File Reference

Between Exif tags or Iptc datasetsand XMP properties
Exif.Image.ImageWidthXmp.tiff.ImageWidth
Exif.Image.ImageLengthXmp.tiff.ImageLength
Exif.Image.BitsPerSampleXmp.tiff.BitsPerSample
Exif.Image.CompressionXmp.tiff.Compression
Exif.Image.PhotometricInterpretationXmp.tiff.PhotometricInterpretation
Exif.Image.OrientationXmp.tiff.Orientation
Exif.Image.SamplesPerPixelXmp.tiff.SamplesPerPixel
Exif.Image.PlanarConfigurationXmp.tiff.PlanarConfiguration
Exif.Image.YCbCrSubSamplingXmp.tiff.YCbCrSubSampling
Exif.Image.YCbCrPositioningXmp.tiff.YCbCrPositioning
Exif.Image.XResolutionXmp.tiff.XResolution
Exif.Image.YResolutionXmp.tiff.YResolution
Exif.Image.ResolutionUnitXmp.tiff.ResolutionUnit
Exif.Image.TransferFunctionXmp.tiff.TransferFunction
Exif.Image.WhitePointXmp.tiff.WhitePoint
Exif.Image.PrimaryChromaticitiesXmp.tiff.PrimaryChromaticities
Exif.Image.YCbCrCoefficientsXmp.tiff.YCbCrCoefficients
Exif.Image.ReferenceBlackWhiteXmp.tiff.ReferenceBlackWhite
Exif.Image.DateTimeXmp.xmp.ModifyDate
Exif.Image.ImageDescriptionXmp.dc.description
Exif.Image.MakeXmp.tiff.Make
Exif.Image.ModelXmp.tiff.Model
Exif.Image.SoftwareXmp.tiff.Software
Exif.Image.ArtistXmp.dc.creator
Exif.Image.RatingXmp.xmp.Rating
Exif.Image.CopyrightXmp.dc.rights
Exif.Photo.ExifVersionXmp.exif.ExifVersion
Exif.Photo.FlashpixVersionXmp.exif.FlashpixVersion
Exif.Photo.ColorSpaceXmp.exif.ColorSpace
Exif.Photo.ComponentsConfigurationXmp.exif.ComponentsConfiguration
Exif.Photo.CompressedBitsPerPixelXmp.exif.CompressedBitsPerPixel
Exif.Photo.PixelXDimensionXmp.exif.PixelXDimension
Exif.Photo.PixelYDimensionXmp.exif.PixelYDimension
Exif.Photo.UserCommentXmp.exif.UserComment
Exif.Photo.RelatedSoundFileXmp.exif.RelatedSoundFile
Exif.Photo.DateTimeOriginalXmp.photoshop.DateCreated
Exif.Photo.DateTimeDigitizedXmp.xmp.CreateDate
Exif.Photo.ExposureTimeXmp.exif.ExposureTime
Exif.Photo.FNumberXmp.exif.FNumber
Exif.Photo.ExposureProgramXmp.exif.ExposureProgram
Exif.Photo.SpectralSensitivityXmp.exif.SpectralSensitivity
Exif.Photo.ISOSpeedRatingsXmp.exif.ISOSpeedRatings
Exif.Photo.OECFXmp.exif.OECF
Exif.Photo.ShutterSpeedValueXmp.exif.ShutterSpeedValue
Exif.Photo.ApertureValueXmp.exif.ApertureValue
Exif.Photo.BrightnessValueXmp.exif.BrightnessValue
Exif.Photo.ExposureBiasValueXmp.exif.ExposureBiasValue
Exif.Photo.MaxApertureValueXmp.exif.MaxApertureValue
Exif.Photo.SubjectDistanceXmp.exif.SubjectDistance
Exif.Photo.MeteringModeXmp.exif.MeteringMode
Exif.Photo.LightSourceXmp.exif.LightSource
Exif.Photo.FlashXmp.exif.Flash
Exif.Photo.FocalLengthXmp.exif.FocalLength
Exif.Photo.SubjectAreaXmp.exif.SubjectArea
Exif.Photo.FlashEnergyXmp.exif.FlashEnergy
Exif.Photo.SpatialFrequencyResponseXmp.exif.SpatialFrequencyResponse
Exif.Photo.FocalPlaneXResolutionXmp.exif.FocalPlaneXResolution
Exif.Photo.FocalPlaneYResolutionXmp.exif.FocalPlaneYResolution
Exif.Photo.FocalPlaneResolutionUnitXmp.exif.FocalPlaneResolutionUnit
Exif.Photo.SubjectLocationXmp.exif.SubjectLocation
Exif.Photo.ExposureIndexXmp.exif.ExposureIndex
Exif.Photo.SensingMethodXmp.exif.SensingMethod
Exif.Photo.FileSourceXmp.exif.FileSource
Exif.Photo.SceneTypeXmp.exif.SceneType
Exif.Photo.CFAPatternXmp.exif.CFAPattern
Exif.Photo.CustomRenderedXmp.exif.CustomRendered
Exif.Photo.ExposureModeXmp.exif.ExposureMode
Exif.Photo.WhiteBalanceXmp.exif.WhiteBalance
Exif.Photo.DigitalZoomRatioXmp.exif.DigitalZoomRatio
Exif.Photo.FocalLengthIn35mmFilmXmp.exif.FocalLengthIn35mmFilm
Exif.Photo.SceneCaptureTypeXmp.exif.SceneCaptureType
Exif.Photo.GainControlXmp.exif.GainControl
Exif.Photo.ContrastXmp.exif.Contrast
Exif.Photo.SaturationXmp.exif.Saturation
Exif.Photo.SharpnessXmp.exif.Sharpness
Exif.Photo.DeviceSettingDescriptionXmp.exif.DeviceSettingDescription
Exif.Photo.SubjectDistanceRangeXmp.exif.SubjectDistanceRange
Exif.Photo.ImageUniqueIDXmp.exif.ImageUniqueID
Exif.GPSInfo.GPSVersionIDXmp.exif.GPSVersionID
Exif.GPSInfo.GPSLatitudeXmp.exif.GPSLatitude
Exif.GPSInfo.GPSLongitudeXmp.exif.GPSLongitude
Exif.GPSInfo.GPSAltitudeRefXmp.exif.GPSAltitudeRef
Exif.GPSInfo.GPSAltitudeXmp.exif.GPSAltitude
Exif.GPSInfo.GPSTimeStampXmp.exif.GPSTimeStamp
Exif.GPSInfo.GPSSatellitesXmp.exif.GPSSatellites
Exif.GPSInfo.GPSStatusXmp.exif.GPSStatus
Exif.GPSInfo.GPSMeasureModeXmp.exif.GPSMeasureMode
Exif.GPSInfo.GPSDOPXmp.exif.GPSDOP
Exif.GPSInfo.GPSSpeedRefXmp.exif.GPSSpeedRef
Exif.GPSInfo.GPSSpeedXmp.exif.GPSSpeed
Exif.GPSInfo.GPSTrackRefXmp.exif.GPSTrackRef
Exif.GPSInfo.GPSTrackXmp.exif.GPSTrack
Exif.GPSInfo.GPSImgDirectionRefXmp.exif.GPSImgDirectionRef
Exif.GPSInfo.GPSImgDirectionXmp.exif.GPSImgDirection
Exif.GPSInfo.GPSMapDatumXmp.exif.GPSMapDatum
Exif.GPSInfo.GPSDestLatitudeXmp.exif.GPSDestLatitude
Exif.GPSInfo.GPSDestLongitudeXmp.exif.GPSDestLongitude
Exif.GPSInfo.GPSDestBearingRefXmp.exif.GPSDestBearingRef
Exif.GPSInfo.GPSDestBearingXmp.exif.GPSDestBearing
Exif.GPSInfo.GPSDestDistanceRefXmp.exif.GPSDestDistanceRef
Exif.GPSInfo.GPSDestDistanceXmp.exif.GPSDestDistance
Exif.GPSInfo.GPSProcessingMethodXmp.exif.GPSProcessingMethod
Exif.GPSInfo.GPSAreaInformationXmp.exif.GPSAreaInformation
Exif.GPSInfo.GPSDifferentialXmp.exif.GPSDifferential
Iptc.Application2.RecordVersionXmp.xmp.Rating
Iptc.Application2.ObjectNameXmp.dc.title
Iptc.Application2.UrgencyXmp.photoshop.Urgency
Iptc.Application2.CategoryXmp.photoshop.Category
Iptc.Application2.SuppCategoryXmp.photoshop.SupplementalCategories
Iptc.Application2.KeywordsXmp.dc.subject
Iptc.Application2.SubLocationXmp.iptc.Location
Iptc.Application2.SpecialInstructionsXmp.photoshop.Instructions
Iptc.Application2.DateCreatedXmp.photoshop.DateCreated
Iptc.Application2.DigitizationDateXmp.xmp.CreateDate
Iptc.Application2.BylineXmp.dc.creator
Iptc.Application2.BylineTitleXmp.photoshop.AuthorsPosition
Iptc.Application2.CityXmp.photoshop.City
Iptc.Application2.ProvinceStateXmp.photoshop.State
Iptc.Application2.CountryCodeXmp.iptc.CountryCode
Iptc.Application2.CountryNameXmp.photoshop.Country
Iptc.Application2.TransmissionReferenceXmp.photoshop.TransmissionReference
Iptc.Application2.HeadlineXmp.photoshop.Headline
Iptc.Application2.CreditXmp.photoshop.Credit
Iptc.Application2.SourceXmp.photoshop.Source
Iptc.Application2.CopyrightXmp.dc.rights
Iptc.Application2.CaptionXmp.dc.description
Iptc.Application2.WriterXmp.photoshop.CaptionWriter