Expected Behavior

Metadata-Extractor will also check for/extract externally specified metadata (EXIF, XMP, and MPEG-7)

Current Behavior

Metadata-Extractor only extracts metadata specified by HEIF itself

Detailed Description

There is potential for externally specified metadata: EXIF, XMP, and MPEG-7. More information on how to get at this data is provided in Annex A of ISO/IEC 23008-12:2017.

Issue originally branched from #362 :
4. cannot get the Exif info from the mdat box, I think this feature has not been implemented yet. :)