Do not read metadata from bob.db packages by hand, use API
Both bob.db.cohface and hci_tagging offer an API for reading metadata, so bob.rppg.base should not do it by hand. This will simplify code in that package and give us some flexibility to optimize metadata storage for a future release. It should be something like:
for f in bob.db.cohface.Database().objects(...):
hr = f.load_face_detection()