# CMTag Types and interfaces for working with Core Media tags. ## Topics ### Creating Tags [`extern CMTag CMTagMakeFromDictionary(CFDictionaryRef dict);`](/documentation/CoreMedia/CMTagMakeFromDictionary) Create a new tag from a dictionary object. [`extern CMTag CMTagMakeWithFlagsValue(CMTagCategory category, uint64_t flagsForTag);`](/documentation/CoreMedia/CMTagMakeWithFlagsValue) Creates a new tag with a given category and a value interpreted as a 64-bit flag field. [`extern CMTag CMTagMakeWithFloat64Value(CMTagCategory category, Float64 value);`](/documentation/CoreMedia/CMTagMakeWithFloat64Value) Creates a new tag with a given category and a 64-bit floating point value. [`extern CMTag CMTagMakeWithOSTypeValue(CMTagCategory category, OSType value);`](/documentation/CoreMedia/CMTagMakeWithOSTypeValue) Creates a new tag with a given category and a 64-bit value for use by the framework. [`extern CMTag CMTagMakeWithSInt64Value(CMTagCategory category, int64_t value);`](/documentation/CoreMedia/CMTagMakeWithSInt64Value) Creates a new tag with a given category and a 64-bit signed integer. ### Tag Categories [`enum CMTagCategory : FourCharCode;`](/documentation/CoreMedia/CMTagCategory) A 64-bit representation of a tag’s category. ### Tag Data Types [`enum CMTagDataType : uint32_t;`](/documentation/CoreMedia/CMTagDataType) The data type of a tag’s value. ### Inspecting Tags [`extern CFStringRefCMTagCopyDescription(CFAllocatorRef allocator, CMTag tag);`](/documentation/CoreMedia/CMTagCopyDescription) Copies the description of a tag to a new string. [`static Boolean CMTagIsValid(CMTag tag);`](/documentation/CoreMedia/CMTagIsValid) Whether the provided tag is valid. [`static CMTagCategory CMTagGetCategory(CMTag tag);`](/documentation/CoreMedia/CMTagGetCategory) Retrieves the category of a tag. [`extern CMTagDataType CMTagGetValueDataType(CMTag tag);`](/documentation/CoreMedia/CMTagGetValueDataType) Retrieves the data type of a tag. [`static Boolean CMTagHasCategory(CMTag tag, CMTagCategory category);`](/documentation/CoreMedia/CMTagHasCategory) Checks if a tag contains a specific category. [`extern Boolean CMTagHasFlagsValue(CMTag tag);`](/documentation/CoreMedia/CMTagHasFlagsValue) Whether a given tag contains a value for a 64-bit flag field. [`extern Boolean CMTagHasFloat64Value(CMTag tag);`](/documentation/CoreMedia/CMTagHasFloat64Value) Whether a given tag contains a value for a 64-bit floating point number. [`extern Boolean CMTagHasOSTypeValue(CMTag tag);`](/documentation/CoreMedia/CMTagHasOSTypeValue) Whether a given tag contains a value for use by the operating system. [`extern Boolean CMTagHasSInt64Value(CMTag tag);`](/documentation/CoreMedia/CMTagHasSInt64Value) Whether a given tag contains a value for a signed 64-bit integer. ### Retrieving Tag Values [`extern CFDictionaryRefCMTagCopyAsDictionary(CMTag tag, CFAllocatorRef allocator);`](/documentation/CoreMedia/CMTagCopyAsDictionary) Copies an existing tag to a new dictionary object. [`extern uint64_t CMTagGetFlagsValue(CMTag tag);`](/documentation/CoreMedia/CMTagGetFlagsValue) Retrieves a tag’s value as a 64-bit field flag. [`extern Float64 CMTagGetFloat64Value(CMTag tag);`](/documentation/CoreMedia/CMTagGetFloat64Value) Retrieves a tag’s value as a 64-bit floating point number. [`extern OSType CMTagGetOSTypeValue(CMTag tag);`](/documentation/CoreMedia/CMTagGetOSTypeValue) Retrieves a tag’s value for use by the operating system. [`extern int64_t CMTagGetSInt64Value(CMTag tag);`](/documentation/CoreMedia/CMTagGetSInt64Value) Retrieves a tag’s value as a signed 64-bit integer. [`static CMTagValue CMTagGetValue(CMTag tag);`](/documentation/CoreMedia/CMTagGetValue) Retrieves a tag’s value as an uninterpreted 64-bit wide unsigned integer. ### Comparison and Equality [`extern Boolean CMTagEqualToTag(CMTag tag1, CMTag tag2);`](/documentation/CoreMedia/CMTagEqualToTag) Compares two tags for strict equality. [`extern CFComparisonResult CMTagCompare(CMTag tag1, CMTag tag2);`](/documentation/CoreMedia/CMTagCompare) Compares two tags in terms of partial equality. [`static Boolean CMTagCategoryEqualToTagCategory(CMTag tag1, CMTag tag2);`](/documentation/CoreMedia/CMTagCategoryEqualToTagCategory) Compares two tags’s categories for equality. [`static Boolean CMTagCategoryValueEqualToValue(CMTag tag1, CMTag tag2);`](/documentation/CoreMedia/CMTagCategoryValueEqualToValue) Compares two tags’s values for equality. [`extern CFHashCode CMTagHash(CMTag tag);`](/documentation/CoreMedia/CMTagHash) Generates a hash identifier for a tag. ### Types [`struct CMTag;`](/documentation/CoreMedia/CMTag-c.struct) A tag representing additional metadata on tagged media buffers. [`class CMTag`](/documentation/CoreMedia/CMTag-swift.class) A tag to set additional metadata on media buffers. [`typedef uint64_t CMTagValue;`](/documentation/CoreMedia/CMTagValue) The type used to represent tag values. ### Constants [`extern CFStringRef const kCMTagCategoryKey;`](/documentation/CoreMedia/kCMTagCategoryKey) A constant for use as a key during tag creation from a dictionary, whose value is the tag’s category. [`extern CFStringRef const kCMTagDataTypeKey;`](/documentation/CoreMedia/kCMTagDataTypeKey) A constant for use as a key during tag creation from a dictionary, whose value is the tag’s data type. [`extern CFStringRef const kCMTagValueKey;`](/documentation/CoreMedia/kCMTagValueKey) A constant for use as a key during tag creation from a dictionary, whose value is the tag’s contained value. [`extern const CMTag kCMTagInvalid;`](/documentation/CoreMedia/kCMTagInvalid) A constant representing an invalid tag. [Tag Values](/documentation/CoreMedia/tag-values) ### Errors [`enum CMTagError : OSStatus;`](/documentation/CoreMedia/CMTagError) Core media tagging errors reported by the framework. --- 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)