---
title: CMFormatDescription.Extensions
framework: coremedia
role: symbol
role_heading: Structure
path: coremedia/cmformatdescription/extensions-swift.struct
---

# CMFormatDescription.Extensions

A type that describes format description extensions.

## Declaration

```swift
struct Extensions
```

## Topics

### Creating Extensions

- [init()](coremedia/cmformatdescription/extensions-swift.struct/init().md)
- [init(base:)](coremedia/cmformatdescription/extensions-swift.struct/init(base:).md)

### Finding Extension Elements

- [subscript(_:)](coremedia/cmformatdescription/extensions-swift.struct/subscript(_:)-1c6vg.md)
- [subscript(_:)](coremedia/cmformatdescription/extensions-swift.struct/subscript(_:)-80zh8.md)

### Constants

- [CMFormatDescription.Extensions.Key](coremedia/cmformatdescription/extensions-swift.struct/key.md)
- [CMFormatDescription.Extensions.Value](coremedia/cmformatdescription/extensions-swift.struct/value.md)

## Relationships

### Conforms To

- [Collection](swift/collection.md)
- [Copyable](swift/copyable.md)
- [Equatable](swift/equatable.md)
- [Escapable](swift/escapable.md)
- [Hashable](swift/hashable.md)
- [Sendable](swift/sendable.md)
- [SendableMetatype](swift/sendablemetatype.md)
- [Sequence](swift/sequence.md)

## See Also

### Constants

- [extensionKeysCommonWithImageBuffers](coremedia/cmformatdescription/extensionkeyscommonwithimagebuffers.md)
- [typeID](coremedia/cmformatdescription/typeid.md)
- [CMFormatDescription.MediaType](coremedia/cmformatdescription/mediatype-swift.struct.md)
- [CMFormatDescription.MediaSubType](coremedia/cmformatdescription/mediasubtype-swift.struct.md)
- [CMFormatDescription.TimeCode](coremedia/cmformatdescription/timecode.md)
- [CMFormatDescription.EqualityMask](coremedia/cmformatdescription/equalitymask.md)
- [CMFormatDescription.ParameterSetCollection](coremedia/cmformatdescription/parametersetcollection.md)