The common key of the metadata item.
- iOS 4.0+
- macOS 10.7+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 6.0+
This property contains the key that most closely corresponds to the key in the
key property but that belongs to the common key space (
AVMetadata) as opposed to a format-specific key space. You can use this key to locate metadata items irrespective of the underlying media format.