Struct AVAssetReaderOutputMetadataAdaptor

Source

pub struct AVAssetReaderOutputMetadataAdaptor { /* private fields */ }

Available on crate feature AVAssetReaderOutput only.

Expand description

Apple’s documentation

Implementations§

Source §

pub unsafe fn assetReaderOutputMetadataAdaptorWithAssetReaderTrackOutput( track_output: &AVAssetReaderTrackOutput, ) -> Retained<Self>

Creates a new timed metadata group adaptor for retrieving timed metadata group objects from an asset reader output.

Parameter assetReaderOutput: An instance of AVAssetReaderTrackOutput that vends sample buffers containing metadata, e.g. an AVAssetReaderTrackOutput object initialized with a track of media type AVMediaTypeMetadata and nil outputSettings.

Returns: An instance of AVAssetReaderOutputMetadataAdaptor

It is an error to create a timed metadata group adaptor with an asset reader output that does not vend metadata. It is also an error to create a timed metadata group adaptor with an asset reader output whose asset reader has already started reading, or an asset reader output that already has been used to initialize another timed metadata group adaptor.

Clients should not mix calls to -[AVAssetReaderTrackOutput copyNextSampleBuffer] and -[AVAssetReaderOutputMetadataAdaptor nextTimedMetadataGroup]. Once an AVAssetReaderTrackOutput instance has been used to initialize an AVAssetReaderOutputMetadataAdaptor, calling -copyNextSampleBuffer on that instance will result in an exception being thrown.

Source

pub unsafe fn initWithAssetReaderTrackOutput( this: Allocated<Self>, track_output: &AVAssetReaderTrackOutput, ) -> Retained<Self>

Creates a new timed metadata group adaptor for retrieving timed metadata group objects from an asset reader output.

Parameter assetReaderOutput: An instance of AVAssetReaderTrackOutput that vends sample buffers containing metadata, e.g. an AVAssetReaderTrackOutput object initialized with a track of media type AVMediaTypeMetadata and nil outputSettings.

Returns: An instance of AVAssetReaderOutputMetadataAdaptor

It is an error to create a timed metadata group adaptor with an asset reader output that does not vend metadata. It is also an error to create a timed metadata group adaptor with an asset reader output whose asset reader has already started reading, or an asset reader output that already has been used to initialize another timed metadata group adaptor.

Clients should not mix calls to -[AVAssetReaderTrackOutput copyNextSampleBuffer] and -[AVAssetReaderOutputMetadataAdaptor nextTimedMetadataGroup]. Once an AVAssetReaderTrackOutput instance has been used to initialize an AVAssetReaderOutputMetadataAdaptor, calling -copyNextSampleBuffer on that instance will result in an exception being thrown.

This method throws an exception if the track’s output was used to initialize another adaptor or if the track output’s asset reader has already started reading.

Source

pub unsafe fn assetReaderTrackOutput( &self, ) -> Retained<AVAssetReaderTrackOutput>

The asset reader track output from which the receiver pulls timed metadata groups.

Source

pub unsafe fn nextTimedMetadataGroup( &self, ) -> Option<Retained<AVTimedMetadataGroup>>

Available on crate feature AVTimedMetadataGroup only.

Returns the next timed metadata group for the asset reader output, synchronously.

Returns: An instance of AVTimedMetadataGroup, representing the next logical segment of metadata coming from the source asset reader output.

This method will return nil when all timed metadata groups have been read from the asset reader output, or if there is an error that prevents the timed metadata group adaptor from reading more timed metadata groups. When this method returns nil, clients should check the value of the associated AVAssetReader’s status property to determine why no more samples could be read.

Unlike -[AVAssetReaderTrackOutput copyNextSampleBuffer], this method returns an autoreleased object.

Before calling this method, you must ensure that the output which underlies the receiver is attached to an AVAssetReader via a prior call to -addOutput: and that -startReading has been called on the asset reader.

This method throws an exception if track output is not attached to an asset reader and reading has not yet begun.

Methods from Deref<Target = NSObject>§

Source

pub fn doesNotRecognizeSelector(&self, sel: Sel) -> !

Handle messages the object doesn’t recognize.

See Apple’s documentation for details.

Methods from Deref<Target = AnyObject>§

Source

pub fn class(&self) -> &'static AnyClass

Dynamically find the class of this object.

§Panics

May panic if the object is invalid (which may be the case for objects returned from unavailable init/new methods).

§Example

Check that an instance of NSObject has the precise class NSObject.

use objc2::ClassType;
use objc2::runtime::NSObject;

let obj = NSObject::new();
assert_eq!(obj.class(), NSObject::class());

Source

pub unsafe fn get_ivar<T>(&self, name: &str) -> &T
where T: Encode,

👎Deprecated: this is difficult to use correctly, use Ivar::load instead.

Use Ivar::load instead.

§Safety

The object must have an instance variable with the given name, and it must be of type T.

See Ivar::load_ptr for details surrounding this.

Source

pub fn downcast_ref<T>(&self) -> Option<&T>
where T: DowncastTarget,

Attempt to downcast the object to a class of type T.

This is the reference-variant. Use Retained::downcast if you want to convert a retained object to another type.

§Mutable classes

Some classes have immutable and mutable variants, such as NSString and NSMutableString.

When some Objective-C API signature says it gives you an immutable class, it generally expects you to not mutate that, even though it may technically be mutable “under the hood”.

So using this method to convert a NSString to a NSMutableString, while not unsound, is generally frowned upon unless you created the string yourself, or the API explicitly documents the string to be mutable.

See Apple’s documentation on mutability and on isKindOfClass: for more details.

§Generic classes

Objective-C generics are called “lightweight generics”, and that’s because they aren’t exposed in the runtime. This makes it impossible to safely downcast to generic collections, so this is disallowed by this method.

You can, however, safely downcast to generic collections where all the type-parameters are AnyObject.

§Panics

This works internally by calling isKindOfClass:. That means that the object must have the instance method of that name, and an exception will be thrown (if CoreFoundation is linked) or the process will abort if that is not the case. In the vast majority of cases, you don’t need to worry about this, since both root objects NSObject and NSProxy implement this method.

§Examples

Cast an NSString back and forth from NSObject.

use objc2::rc::Retained;
use objc2_foundation::{NSObject, NSString};

let obj: Retained<NSObject> = NSString::new().into_super();
let string = obj.downcast_ref::<NSString>().unwrap();
// Or with `downcast`, if we do not need the object afterwards
let string = obj.downcast::<NSString>().unwrap();

Try (and fail) to cast an NSObject to an NSString.

use objc2_foundation::{NSObject, NSString};

let obj = NSObject::new();
assert!(obj.downcast_ref::<NSString>().is_none());

Try to cast to an array of strings.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);
// This is invalid and doesn't type check.
let arr = arr.downcast_ref::<NSArray<NSString>>();

This fails to compile, since it would require enumerating over the array to ensure that each element is of the desired type, which is a performance pitfall.

Downcast when processing each element instead.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);

for elem in arr {
    if let Some(data) = elem.downcast_ref::<NSString>() {
        // handle `data`
    }
}