The abstract class used to model timed audiovisual media such as videos and sounds.
- iOS 4.0+
- macOS 10.7+
- tvOS 9.0+
AVAsset defines the collective properties of the tracks that comprise the asset. You create an
AVAsset by initializing it with a local or remote URL pointing to a media resource, as shown in the following example:
AVAsset is an abstract class, so when you create an asset as shown in the example, you’re actually creating an instance of one of its concrete subclasses called
AVURLAsset. In many cases this is a suitable way of creating an asset, but you can also directly instantiate an
AVURLAsset when you need more fine-grained control over its initialization. The initializer for
AVURLAsset accepts an options dictionary, with which you tailor the asset’s initialization to your particular use case. For instance, if you’re creating an asset for an HLS stream, you may want to prevent it from retrieving its media when a user is connected to a cellular network. You can do this as shown in the following example:
You can also instantiate an asset using other concrete subclasses that extend the basic model for audiovisual media in useful ways, as
AVComposition does for temporal editing.
Because of the nature of timed audiovisual media, upon successful initialization of an asset, some or all of the values for its keys may not be immediately available. The value of any key can be requested at any time, and the asset always returns its value synchronously, although it may have to block the calling thread to do so. To avoid blocking, you can register your interest in particular keys and be notified when their values become available. For further details, see
To play an instance of
AVAsset, initialize an instance of
AVPlayer with it, use the player item to set up its presentation state (such as whether only a limited
time of the asset should be played), and provide the player item to an
AVPlayer object according to whether the item is to be played by itself or with a collection of other items.
You can insert
AVAsset objects into an
AVMutable object to assemble audiovisual constructs from one or more source assets.
It isn't currently possible to subclass
AVAsset to handle streaming protocols or file formats that aren't supported by the framework.