# CMTagCollection Objective-C types and interfaces for working with Core Media tag collections. ## Topics ### Creating Collections [`extern OSStatus CMTagCollectionCreate(CFAllocatorRef allocator, const CMTag *tags, CMItemCount tagCount, CMTagCollectionRef*newCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreate) Creates a new tag collection from an existing C-style array of tags. [`extern OSStatus CMTagCollectionCreateMutable(CFAllocatorRef allocator, CFIndex capacity, CMMutableTagCollectionRef*newMutableCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreateMutable) Creates a new, mutable, empty tag collection. [`extern OSStatus CMTagCollectionCreateFromData(CFDataRef data, CFAllocatorRef allocator, CMTagCollectionRef*newCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreateFromData) Creates a new tag collection from an existing Core Foundation data instance. [`extern OSStatus CMTagCollectionCreateFromDictionary(CFDictionaryRef dict, CFAllocatorRef allocator, CMTagCollectionRef*newCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreateFromDictionary) Creates a new tag collection from an existing Core Foundation dictionary. ### Converting to Other Types [`extern CFDataRefCMTagCollectionCopyAsData(CMTagCollectionRef tagCollection, CFAllocatorRef allocator);`](/documentation/CoreMedia/CMTagCollectionCopyAsData) Creates a new Core Foundation data instance from a tag collection. [`extern CFDictionaryRefCMTagCollectionCopyAsDictionary(CMTagCollectionRef tagCollection, CFAllocatorRef allocator);`](/documentation/CoreMedia/CMTagCollectionCopyAsDictionary) Creates a new Core Foundation dictionary from a tag collection. ### Inspecting Collections [`extern CMItemCount CMTagCollectionGetCount(CMTagCollectionRef tagCollection);`](/documentation/CoreMedia/CMTagCollectionGetCount) Gets the number of tags in a tag collection. [`extern CMItemCount CMTagCollectionCountTagsWithFilterFunction(CMTagCollectionRef tagCollection, CMTagCollectionTagFilterFunction filterApplier, void *context);`](/documentation/CoreMedia/CMTagCollectionCountTagsWithFilterFunction) Counts the number of tags in a collection matching an evaluation function. [`extern Boolean CMTagCollectionIsEmpty(CMTagCollectionRef tagCollection);`](/documentation/CoreMedia/CMTagCollectionIsEmpty) Checks if a tag collection has no elements. [`extern OSStatus CMTagCollectionGetTags(CMTagCollectionRef tagCollection, CMTag *tagBuffer, CMItemCount tagBufferCount, CMItemCount *numberOfTagsCopied);`](/documentation/CoreMedia/CMTagCollectionGetTags) Retrieves an arbitrary number of tags from the collection. [`extern OSStatus CMTagCollectionGetTagsWithCategory(CMTagCollectionRef tagCollection, CMTagCategory category, CMTag *tagBuffer, CMItemCount tagBufferCount, CMItemCount *numberOfTagsCopied);`](/documentation/CoreMedia/CMTagCollectionGetTagsWithCategory) Retrieves a C-style array of tags with a given category from a tag collection. [`extern OSStatus CMTagCollectionGetTagsWithFilterFunction(CMTagCollectionRef tagCollection, CMTag *tagBuffer, CMItemCount tagBufferCount, CMItemCount *numberOfTagsCopied, CMTagCollectionTagFilterFunction filter, void *context);`](/documentation/CoreMedia/CMTagCollectionGetTagsWithFilterFunction) Gets all tags in a collection matching an evaluation function. [`extern Boolean CMTagCollectionContainsCategory(CMTagCollectionRef tagCollection, CMTagCategory category);`](/documentation/CoreMedia/CMTagCollectionContainsCategory) Determines if a tag collection contains tags for a given category. [`extern CMItemCount CMTagCollectionGetCountOfCategory(CMTagCollectionRef tagCollection, CMTagCategory category);`](/documentation/CoreMedia/CMTagCollectionGetCountOfCategory) Retrieves the number of tags in the collection matching a given category. [`extern Boolean CMTagCollectionContainsTag(CMTagCollectionRef tagCollection, CMTag tag);`](/documentation/CoreMedia/CMTagCollectionContainsTag) Determines if a tag collection contains a specific tag. [`extern Boolean CMTagCollectionContainsSpecifiedTags(CMTagCollectionRef tagCollection, const CMTag *containedTags, CMItemCount containedTagCount);`](/documentation/CoreMedia/CMTagCollectionContainsSpecifiedTags) Determines if a tag collection contains a subset of tags. [`extern Boolean CMTagCollectionContainsTagsOfCollection(CMTagCollectionRef tagCollection, CMTagCollectionRef containedTagCollection);`](/documentation/CoreMedia/CMTagCollectionContainsTagsOfCollection) Determines if one collection of tags contains every tag from another collection. [`extern CFStringRefCMTagCollectionCopyDescription(CFAllocatorRef allocator, CMTagCollectionRef tagCollection);`](/documentation/CoreMedia/CMTagCollectionCopyDescription) Retrieves a copy of the tag collection’s description. [`extern CFTypeID CMTagCollectionGetTypeID();`](/documentation/CoreMedia/CMTagCollectionGetTypeID) Retrieves the internal type ID for tag collections. ### Modifying Collection Tags [`extern OSStatus CMTagCollectionAddTag(CMMutableTagCollectionRef tagCollection, CMTag tagToAdd);`](/documentation/CoreMedia/CMTagCollectionAddTag) Adds a new tag to an existing collection. [`extern OSStatus CMTagCollectionAddTagsFromArray(CMMutableTagCollectionRef tagCollection, CMTag *tags, CMItemCount tagCount);`](/documentation/CoreMedia/CMTagCollectionAddTagsFromArray) Adds the tags contained in a C-style array to a tag collection. [`extern OSStatus CMTagCollectionAddTagsFromCollection(CMMutableTagCollectionRef tagCollection, CMTagCollectionRef collectionWithTagsToAdd);`](/documentation/CoreMedia/CMTagCollectionAddTagsFromCollection) Add the tags contained in one collection to another. [`extern OSStatus CMTagCollectionRemoveAllTags(CMMutableTagCollectionRef tagCollection);`](/documentation/CoreMedia/CMTagCollectionRemoveAllTags) Removes all tags from a collection. [`extern OSStatus CMTagCollectionRemoveAllTagsOfCategory(CMMutableTagCollectionRef tagCollection, CMTagCategory category);`](/documentation/CoreMedia/CMTagCollectionRemoveAllTagsOfCategory) Removes all tags of a given category from a collection. [`extern OSStatus CMTagCollectionRemoveTag(CMMutableTagCollectionRef tagCollection, CMTag tagToRemove);`](/documentation/CoreMedia/CMTagCollectionRemoveTag) Removes a specific tag from a collection. ### Deriving New Collections [`extern OSStatus CMTagCollectionCreateCopy(CMTagCollectionRef tagCollection, CFAllocatorRef allocator, CMTagCollectionRef*newCollectionCopyOut);`](/documentation/CoreMedia/CMTagCollectionCreateCopy) Creates a copy of a tag collection. [`extern OSStatus CMTagCollectionCreateMutableCopy(CMTagCollectionRef tagCollection, CFAllocatorRef allocator, CMMutableTagCollectionRef*newMutableCollectionCopyOut);`](/documentation/CoreMedia/CMTagCollectionCreateMutableCopy) Creates a new mutable copy from an existing tag collection. [`extern OSStatus CMTagCollectionCopyTagsOfCategories(CFAllocatorRef allocator, CMTagCollectionRef tagCollection, const CMTagCategory *categories, CMItemCount categoriesCount, CMTagCollectionRef*collectionWithTagsOfCategories);`](/documentation/CoreMedia/CMTagCollectionCopyTagsOfCategories) Creates a new tag collection from an existing collection, copying all tags which match a list of categories. [`extern OSStatus CMTagCollectionCreateUnion(CMTagCollectionRef tagCollection1, CMTagCollectionRef tagCollection2, CMTagCollectionRef*tagCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreateUnion) Creates a new tag collection containing all tags from two collections without duplicates. [`extern OSStatus CMTagCollectionCreateDifference(CMTagCollectionRef tagCollectionMinuend, CMTagCollectionRef tagCollectionSubtrahend, CMTagCollectionRef*tagCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreateDifference) Creates a new tag collection with the difference of two existing collections. [`extern OSStatus CMTagCollectionCreateExclusiveOr(CMTagCollectionRef tagCollection1, CMTagCollectionRef tagCollection2, CMTagCollectionRef*tagCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreateExclusiveOr) Creates a new tag collection from two existing tag collections, copying elements which are in one collection or the other, but not both. [`extern OSStatus CMTagCollectionCreateIntersection(CMTagCollectionRef tagCollection1, CMTagCollectionRef tagCollection2, CMTagCollectionRef*tagCollectionOut);`](/documentation/CoreMedia/CMTagCollectionCreateIntersection) Creates a new tag collection containing only the tags from two existing collections which match. ### Iterating Over Tags [`extern void CMTagCollectionApply(CMTagCollectionRef tagCollection, CMTagCollectionApplierFunction applier, void *context);`](/documentation/CoreMedia/CMTagCollectionApply) Applies a function to all tags in a collection. [`extern CMTag CMTagCollectionApplyUntil(CMTagCollectionRef tagCollection, CMTagCollectionTagFilterFunction applier, void *context);`](/documentation/CoreMedia/CMTagCollectionApplyUntil) Applies a Boolean function to tags in a collection, stopping when it returns true. ### Types [`typedef const struct OpaqueCMTagCollection * CMTagCollectionRef;`](/documentation/CoreMedia/CMTagCollectionRef) A reference to a tag collection. [`typedef struct OpaqueCMTagCollection * CMMutableTagCollectionRef;`](/documentation/CoreMedia/CMMutableTagCollectionRef) A mutable reference to a tag collection. [`typedef void (*)(struct CMTag, void *) CMTagCollectionApplierFunction;`](/documentation/CoreMedia/CMTagCollectionApplierFunction) A type for function application over elements of a tag collection. [`typedef unsigned char (*)(struct CMTag, void *) CMTagCollectionTagFilterFunction;`](/documentation/CoreMedia/CMTagCollectionTagFilterFunction) A type for filtering of tag collections. ### Constants [`extern CFStringRef const kCMTagCollectionTagsArrayKey;`](/documentation/CoreMedia/kCMTagCollectionTagsArrayKey) A dictionary key for assigning tag collections to. ### Errors [`enum CMTagCollectionError : OSStatus;`](/documentation/CoreMedia/CMTagCollectionError) Error codes returned by Core Media when working with tag collections. --- Copyright © 2026 Apple Inc. 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