---
title: Key_namespace
framework: quicktime-file-format
role: symbol
role_heading: Data field
path: quicktime-file-format/metadata_key_declaration_atom/key_namespace
---

# Key_namespace

A 32-bit identifier describing the domain and the structure of the key value.

## Overview

Overview For example, this could indicate that key_value is a reverse-address style string (such as “com.apple.quicktime.ISO6709”), a binary four-character code (such as a 'cprt' user data key), a Uniform Resource Identifier (URI), or other structures (such as native formats from other metadata standards). New key namespaces must be registered but because a reverse-address style string can often be used, using the reverse-address key namespace may be sufficient for most uses.

## See Also

### Data fields

- [Size](quicktime-file-format/metadata_key_declaration_atom/size.md)
- [Type](quicktime-file-format/metadata_key_declaration_atom/type.md)
- [Key_value array](quicktime-file-format/metadata_key_declaration_atom/key_value_array.md)