Contents

AVMediaCharacteristic

A structure that defines media data characteristics.

Declaration

struct AVMediaCharacteristic

Discussion

QuickTime Movie and MPEG-4 video files may contain tracks that provide tagged media characteristics to indicate a purpose, trait, or feature of the track’s media. For example, an audio track that mixes original program content with additional narrative descriptions of visual action may have the media characteristic public.accessibility.describes-video to distinguish it from other audio tracks stored in the same file that don’t contain additional narrative.

You inspect the tagged media characteristics of a track as shown below:

NSArray *userDataItems = [myAVAssetTrack metadataForFormat:AVMetadataFormatQuickTimeUserData];
NSArray *trackTaggedMediaCharacteristics = [AVMetadataItem metadataItemsFromArray: userDataItems
        withKey: AVMetadataQuickTimeUserDataKeyTaggedCharacteristic
        keySpace: AVMetadataKeySpaceQuickTimeUserData];
for (AVMetadataItem *metadataItem in trackTaggedMediaCharacteristics) {
     NSString *thisTrackMediaCharacteristic = [metadataItem stringValue];
}

You write tagged media characteristics to files of type mov and m4v by using an instance of AVAssetWriter. You indicate tagged characteristics for a track by setting metadata on its associated asset writer input as shown below:

AVMutableMetadataItem *myTaggedMediaCharacteristic = [[AVMutableMetadataItem alloc] init];
[myTaggedMediaCharacteristic setKey:AVMetadataQuickTimeUserDataKeyTaggedCharacteristic];
[myTaggedMediaCharacteristic setKeySpace:AVMetadataKeySpaceQuickTimeUserData];
[myTaggedMediaCharacteristic setValue:aMeaningfulCharacteristicAsNSString];
[myMutableArrayOfMetadata addObject:myTaggedMediaCharacteristic];
[myAssetWriterInput setMetadata:myMutableArrayOfMetadata];

Topics

Visual

Audible

Legible

Content

Initializers

See Also

Media types