# CMIOExtensionStreamFormat An object that describes the format of a media stream. ``` class CMIOExtensionStreamFormat ``` ## Topics ### Creating a Stream Format [`convenience init(formatDescription: CMFormatDescription, maxFrameDuration: CMTime, minFrameDuration: CMTime, validFrameDurations: [CMTime]?)`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/init(formatDescription:maxFrameDuration:minFrameDuration:validFrameDurations:)) Creates a stream format with a format description and frame durations. [`+ (instancetype) streamFormatWithFormatDescription:(CMFormatDescriptionRef) formatDescription maxFrameDuration:(CMTime) maxFrameDuration minFrameDuration:(CMTime) minFrameDuration validFrameDurations:(NSArray *) validFrameDurations;`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/streamFormatWithFormatDescription:maxFrameDuration:minFrameDuration:validFrameDurations:) Returns a new stream format with a format description and frame durations. [`- (instancetype) initWithFormatDescription:(CMFormatDescriptionRef) formatDescription maxFrameDuration:(CMTime) maxFrameDuration minFrameDuration:(CMTime) minFrameDuration validFrameDurations:(NSArray *) validFrameDurations;`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/initWithFormatDescription:maxFrameDuration:minFrameDuration:validFrameDurations:) Creates a stream format with a format description and frame durations. ### Configuring Frame Durations [`var minFrameDuration: CMTime`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/minFrameDuration) The minimum frame duration a stream supports. [`var maxFrameDuration: CMTime`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/maxFrameDuration) The maximum duration a stream supports. [`var validFrameDurations: [CMTime]?`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/validFrameDurations-707st) An array of frame durations the stream supports. [`@property (atomic, strong, readonly, nullable) NSArray * validFrameDurations;`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/validFrameDurations-4rbay) An array of frame durations the stream supports. ### Accessing the Format Description [`var formatDescription: CMFormatDescription`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/formatDescription) A description of the format of the stream’s media samples. ### Initializers [`init?(coder: NSCoder)`](/documentation/CoreMediaIO/CMIOExtensionStreamFormat/init(coder:)) ## Relationships ### Conforms To [`CVarArg`](/documentation/Swift/CVarArg) [`NSSecureCoding`](/documentation/Foundation/NSSecureCoding) [`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol) [`Hashable`](/documentation/Swift/Hashable) [`NSCopying`](/documentation/Foundation/NSCopying) [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`Equatable`](/documentation/Swift/Equatable) [`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible) [`NSCoding`](/documentation/Foundation/NSCoding) ### Inherits From [`NSObject-swift.class`](/documentation/ObjectiveC/NSObject-swift.class) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)