There are two general guidelines as far as notifications and threading:
- UI related notifications occur on the main thread.
- Classes or methods that require you create and/or specify a queue will return notifications on that queue.
Beyond those two guidelines (and there are exceptions, which are noted in the reference documentation) you should not assume that a notification will be returned on any specific thread.
If you’re writing a multithreaded application, you can use the NSThread
method isMainThread
or [[NSThread currentThread] isEqual:<#A stored thread reference#>]
to test whether the invocation thread is a thread you expect to perform your work on. You can redirect messages to appropriate threads using methods such as performSelectorOnMainThread:withObject:waitUntilDone:
and performSelector:onThread:withObject:waitUntilDone:modes:
. You could also use dispatch_async
to “bounce” to your blocks on an appropriate queue, either the main queue for UI tasks or a queue you have up for concurrent operations. For more about concurrent operations, see Concurrency Programming Guide; for more about blocks, see Blocks Programming Topics. The AVCam-iOS: Using AVFoundation to Capture Images and Movies sample code is considered the primary example for all AVFoundation functionality and can be consulted for examples of thread and queue usage with AVFoundation.
Generating a Single Image
AVAsset *myAsset = <#An asset#>];
AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:myAsset];
Float64 durationSeconds = CMTimeGetSeconds([myAsset duration]);
CMTime midpoint = CMTimeMakeWithSeconds(durationSeconds/2.0, 600);
NSError *error;
CMTime actualTime;
CGImageRef halfWayImage = [imageGenerator copyCGImageAtTime:midpoint actualTime:&actualTime error:&error];
if (halfWayImage != NULL) {
NSString *actualTimeString = (NSString *)CMTimeCopyDescription(NULL, actualTime);
NSString *requestedTimeString = (NSString *)CMTimeCopyDescription(NULL, midpoint);
NSLog(@"Got halfWayImage: Asked for %@, got %@", requestedTimeString, actualTimeString);
// Do something interesting with the image.
CGImageRelease(halfWayImage);
}
AVAsset *myAsset = <#An asset#>];
// Assume: @property (strong) AVAssetImageGenerator *imageGenerator;
self.imageGenerator = [AVAssetImageGenerator assetImageGeneratorWithAsset:myAsset];
Float64 durationSeconds = CMTimeGetSeconds([myAsset duration]);
CMTime firstThird = CMTimeMakeWithSeconds(durationSeconds/3.0, 600);
CMTime secondThird = CMTimeMakeWithSeconds(durationSeconds*2.0/3.0, 600);
CMTime end = CMTimeMakeWithSeconds(durationSeconds, 600);
NSArray *times = @[NSValue valueWithCMTime:kCMTimeZero],
[NSValue valueWithCMTime:firstThird], [NSValue valueWithCMTime:secondThird],
[NSValue valueWithCMTime:end]];
[imageGenerator generateCGImagesAsynchronouslyForTimes:times
completionHandler:^(CMTime requestedTime, CGImageRef image, CMTime actualTime,
AVAssetImageGeneratorResult result, NSError *error) {
NSString *requestedTimeString = (NSString *)
CFBridgingRelease(CMTimeCopyDescription(NULL, requestedTime));
NSString *actualTimeString = (NSString *)
CFBridgingRelease(CMTimeCopyDescription(NULL, actualTime));
NSLog(@"Requested: %@; actual %@", requestedTimeString, actualTimeString);
if (result == AVAssetImageGeneratorSucceeded) {
// Do something interesting with the image.
}
if (result == AVAssetImageGeneratorFailed) {
NSLog(@"Failed with error: %@", [error localizedDescription]);
}
if (result == AVAssetImageGeneratorCancelled) {
NSLog(@"Canceled");
}
}];
CMTime CMTimeMake (
int64_t value, //表示 當前視頻播放到的第幾楨數(shù)
int32_t timescale //每秒的幀數(shù)
);
CMTime CMTimeMakeWithSeconds(
Float64 seconds, //第幾秒的截圖,是當前視頻播放到的幀數(shù)的具體時間
int32_t preferredTimeScale //首選的時間尺度 "每秒的幀數(shù)"
);
Trimming and Transcoding a Movie
格式轉(zhuǎn)換:
AVAsset *anAsset = <#Get an asset#>;
NSArray *compatiblePresets = [AVAssetExportSession exportPresetsCompatibleWithAsset:anAsset];
if ([compatiblePresets containsObject:AVAssetExportPresetLowQuality]) {
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc]
initWithAsset:anAsset presetName:AVAssetExportPresetLowQuality];
// Implementation continues.
}
exportSession.outputURL = <#A file URL#>;
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
CMTime start = CMTimeMakeWithSeconds(1.0, 600);
CMTime duration = CMTimeMakeWithSeconds(3.0, 600);
CMTimeRange range = CMTimeRangeMake(start, duration);
exportSession.timeRange = range;
[exportSession exportAsynchronouslyWithCompletionHandler:^{
switch ([exportSession status]) {
case AVAssetExportSessionStatusFailed:
NSLog(@"Export failed: %@", [[exportSession error] localizedDescription]);
break;
case AVAssetExportSessionStatusCancelled:
NSLog(@"Export canceled");
break;
default:
break;
}
}];
You can cancel the export by sending the session a cancelExport
message.
The export will fail if you try to overwrite an existing file, or write a file outside of the application’s sandbox. It may also fail if:
There is an incoming phone call
Your application is in the background and another application starts playback
In these situations, you should typically inform the user that the export failed, then allow the user to restart the export.
Playback
To control the playback of assets, you use an AVPlayer
object. During playback, you can use an AVPlayerItem
instance to manage the presentation state of an asset as a whole, and an AVPlayerItemTrack
object to manage the presentation state of an individual track. To display video, you use an AVPlayerLayer
object.
Playing Assets
A player is a controller object that you use to manage playback of an asset, for example starting and stopping playback, and seeking to a particular time. You use an instance of AVPlayer
to play a single asset. You can use an AVQueuePlayer
object to play a number of items in sequence (AVQueuePlayer
is a subclass of AVPlayer
). On OS X you have the option of the using the AVKit framework’s AVPlayerView
class to play the content back within a view.
Multiple player layers: You can create many AVPlayerLayer objects from a single AVPlayer instance, but only the most recently created such layer will display any video content onscreen.
關(guān)系：
Figure 2-2 shows one possibility, with two different players playing the same asset, with different settings. Using the item tracks, you can, for example, disable a particular track during playback (for example, you might not want to play the sound component).
You can initialize a player item with an existing asset, or you can initialize a player item directly from a URL so that you can play a resource at a particular location (AVPlayerItem
will then create and configure an asset for the resource). As with AVAsset
, though, simply initializing a player item doesn’t necessarily mean it’s ready for immediate playback. You can observe (using key-value observing) an item’s status
property to determine if and when it’s ready to play.
Handling Different Types of Asset
The way you configure an asset for playback may depend on the sort of asset you want to play. Broadly speaking, there are two main types: file-based assets, to which you have random access (such as from a local file, the camera roll, or the Media Library), and stream-based assets (HTTP Live Streaming format).
To load and play a file-based asset. There are several steps to playing a file-based asset:
Create an asset using AVURLAsset
.
Create an instance of AVPlayerItem
using the asset.
Associate the item with an instance of AVPlayer
.
Wait until the item’s status
property indicates that it’s ready to play (typically you use key-value observing to receive a notification when the status changes).
To create and prepare an HTTP live stream for playback. Initialize an instance of AVPlayerItem using the URL. (You cannot directly create an AVAsset instance to represent the media in an HTTP Live Stream.)
NSURL *url = [NSURL URLWithString:@"<#Live stream URL#>];
// You may find a test stream at http://devimages.apple.com/iphone/samples/bipbop/bipbopall.m3u8.
self.playerItem = [AVPlayerItem playerItemWithURL:url];
[playerItem addObserver:self forKeyPath:@"status" options:0 context:&ItemStatusContext];
self.player = [AVPlayer playerWithPlayerItem:playerItem];
If you don’t know what kind of URL you have, follow these steps:
Try to initialize an AVURLAsset
using the URL, then load its tracks
key.
If the tracks load successfully, then you create a player item for the asset.If 1 fails, create an AVPlayerItem
directly from the URL.
Observe the player’s status
property to determine whether it becomes playable.
If either route succeeds, you end up with a player item that you can then associate with a player.
Changing the Playback Rate
You change the rate of playback by setting the player’s rate
property.
aPlayer.rate = 0.5;
aPlayer.rate = 2.0;
A value of 1.0 means “play at the natural rate of the current item”. Setting the rate to 0.0 is the same as pausing playback—you can also use pause
.
Items that support reverse playback can use the rate property with a negative number to set the reverse playback rate. You determine the type of reverse play that is supported by using the playerItem properties canPlayReverse
(supports a rate value of -1.0), canPlaySlowReverse
(supports rates between 0.0 and 1.0) and canPlayFastReverse
(supports rate values less than -1.0).
Seeking—Repositioning the Playhead
CMTime fiveSecondsIn = CMTimeMake(5, 1);
[player seekToTime:fiveSecondsIn];
播放結(jié)束妖啥，初始播放位置
// Register with the notification center after creating the player item.
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(playerItemDidReachEnd:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:<#The player item#>];
- (void)playerItemDidReachEnd:(NSNotification *)notification {
[player seekToTime:kCMTimeZero];
}
Important: You should register for KVO change notifications and unregister from KVO change notifications on the main thread. This avoids the possibility of receiving a partial notification if a change is being made on another thread. AV Foundation invokes observeValueForKeyPath:ofObject:change:context:
on the main thread, even if the change operation is made on another thread.
Putting It All Together: Playing a Video File Using AVPlayerLayer
This brief code example illustrates how you can use an AVPlayer
object to play a video file. It shows how to:
- Configure a view to use an AVPlayerLayer layer
- Create an AVPlayer object
- Create an AVPlayerItem object for a file-based asset and use key-value observing to observe its status
- Respond to the item becoming ready to play by enabling a button
- Play the item and then restore the player’s head to the beginning
The Player View
To play the visual component of an asset, you need a view containing an AVPlayerLayer
layer to which the output of an AVPlayer
object can be directed. You can create a simple subclass of UIView
to accommodate this:
#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
@interface PlayerView : UIView
@property (nonatomic) AVPlayer *player;
@end
@implementation PlayerView
+ (Class)layerClass {
return [AVPlayerLayer class];
}
- (AVPlayer*)player {
return [(AVPlayerLayer *)[self layer] player];
}
- (void)setPlayer:(AVPlayer *)player {
[(AVPlayerLayer *)[self layer] setPlayer:player];
}
@end
A Simple View Controller
Assume you have a simple view controller, declared as follows:
@class PlayerView;
@interface PlayerViewController : UIViewController
@property (nonatomic) AVPlayer *player;
@property (nonatomic) AVPlayerItem *playerItem;
@property (nonatomic, weak) IBOutlet PlayerView *playerView;
@property (nonatomic, weak) IBOutlet UIButton *playButton;
- (IBAction)loadAssetFromFile:sender;
- (IBAction)play:sender;
- (void)syncUI;
@end
The syncUI method synchronizes the button’s state with the player’s state:
- (void)viewDidLoad {
[super viewDidLoad];
[self syncUI];
}
- (void)syncUI {
if ((self.player.currentItem != nil) &&
([self.player.currentItem status] == AVPlayerItemStatusReadyToPlay)) {
self.playButton.enabled = YES;
}
else {
self.playButton.enabled = NO;
}
}
- (IBAction)loadAssetFromFile:sender {
NSURL *fileURL = [[NSBundle mainBundle]
URLForResource:<#@"VideoFileName"#> withExtension:<#@"extension"#>];
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:fileURL options:nil];
NSString *tracksKey = @"tracks";
[asset loadValuesAsynchronouslyForKeys:@[tracksKey] completionHandler:
^{
// The completion block goes here.
}];
}
// Define this constant for the key-value observation context.
static const NSString *ItemStatusContext;
// Completion handler block.
dispatch_async(dispatch_get_main_queue(),
^{
NSError *error;
AVKeyValueStatus status = [asset statusOfValueForKey:tracksKey error:&error];
if (status == AVKeyValueStatusLoaded) {
self.playerItem = [AVPlayerItem playerItemWithAsset:asset];
// ensure that this is done before the playerItem is associated with the player
[self.playerItem addObserver:self forKeyPath:@"status"
options:NSKeyValueObservingOptionInitial context:&ItemStatusContext];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(playerItemDidReachEnd:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:self.playerItem];
self.player = [AVPlayer playerWithPlayerItem:self.playerItem];
[self.playerView setPlayer:self.player];
}
else {
// You should deal with the error appropriately.
NSLog(@"The asset's tracks were not loaded:\n%@", [error localizedDescription]);
}
});
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void *)context {
if (context == &ItemStatusContext) {
dispatch_async(dispatch_get_main_queue(),
^{
[self syncUI];
});
return;
}
[super observeValueForKeyPath:keyPath ofObject:object
change:change context:context];
return;
}
- (IBAction)play:sender {
[player play];
}
播放完全后，初始化播放起始位置：
// Register with the notification center after creating the player item.
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(playerItemDidReachEnd:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:[self.player currentItem]];
- (void)playerItemDidReachEnd:(NSNotification *)notification {
[self.player seekToTime:kCMTimeZero];
}
Editing
多視頻文件合成一個視頻文件示意圖：
Using the AVMutableAudioMix
class, you can perform custom audio processing on the audio tracks in your composition, as shown in Figure 3-2：
Creating a Composition
AVMutableComposition *mutableComposition = [AVMutableComposition composition];
// Create the video composition track.
AVMutableCompositionTrack *mutableCompositionVideoTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
// Create the audio composition track.
AVMutableCompositionTrack *mutableCompositionAudioTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
Options for Initializing a Composition Track
When adding new tracks to a composition, you must provide both a media type and a track ID. Although audio and video are the most commonly used media types, you can specify other media types as well, such as AVMediaTypeSubtitle
or AVMediaTypeText
.
Every track associated with some audiovisual data has a unique identifier referred to as a track ID. If you specify kCMPersistentTrackID_Invalid
as the preferred track ID, a unique identifier is automatically generated for you and associated with the track.
Adding Audiovisual Data to a Composition
合成示例：
// You can retrieve AVAssets from a number of places, like the camera roll for example.
AVAsset *videoAsset = <#AVAsset with at least one video track#>;
AVAsset *anotherVideoAsset = <#another AVAsset with at least one video track#>;
// Get the first video track from each asset.
AVAssetTrack *videoAssetTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
AVAssetTrack *anotherVideoAssetTrack = [[anotherVideoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
// Add them both to the composition.
[mutableCompositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,videoAssetTrack.timeRange.duration) ofTrack:videoAssetTrack atTime:kCMTimeZero error:nil];
[mutableCompositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,anotherVideoAssetTrack.timeRange.duration) ofTrack:anotherVideoAssetTrack atTime:videoAssetTrack.timeRange.duration error:nil];
Generating a Volume Ramp
A single AVMutableAudioMix
object can perform custom audio processing on all of the audio tracks in your composition individually. You create an audio mix using the audioMix
class method, and you use instances of the AVMutableAudioMixInputParameters
class to associate the audio mix with specific tracks within your composition. An audio mix can be used to vary the volume of an audio track. The following example displays how to set a volume ramp on a specific audio track to slowly fade the audio out over the duration of the composition:
AVMutableAudioMix *mutableAudioMix = [AVMutableAudioMix audioMix];
// Create the audio mix input parameters object.
AVMutableAudioMixInputParameters *mixParameters = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:mutableCompositionAudioTrack];
// Set the volume ramp to slowly fade the audio out over the duration of the composition.
[mixParameters setVolumeRampFromStartVolume:1.f toEndVolume:0.f timeRange:CMTimeRangeMake(kCMTimeZero, mutableComposition.duration)];
// Attach the input parameters to the audio mix.
mutableAudioMix.inputParameters = @[mixParameters];
Changing the Composition’s Background Color
AVMutableVideoCompositionInstruction *mutableVideoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mutableVideoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, mutableComposition.duration);
mutableVideoCompositionInstruction.backgroundColor = [[UIColor redColor] CGColor];
Applying Opacity Ramps
AVAsset *firstVideoAssetTrack = <#AVAssetTrack representing the first video segment played in the composition#>;
AVAsset *secondVideoAssetTrack = <#AVAssetTrack representing the second video segment played in the composition#>;
// Create the first video composition instruction.
AVMutableVideoCompositionInstruction *firstVideoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
// Set its time range to span the duration of the first video track.
firstVideoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, firstVideoAssetTrack.timeRange.duration);
// Create the layer instruction and associate it with the composition video track.
AVMutableVideoCompositionLayerInstruction *firstVideoLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:mutableCompositionVideoTrack];
// Create the opacity ramp to fade out the first video track over its entire duration.
[firstVideoLayerInstruction setOpacityRampFromStartOpacity:1.f toEndOpacity:0.f timeRange:CMTimeRangeMake(kCMTimeZero, firstVideoAssetTrack.timeRange.duration)];
// Create the second video composition instruction so that the second video track isn't transparent.
AVMutableVideoCompositionInstruction *secondVideoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
// Set its time range to span the duration of the second video track.
secondVideoCompositionInstruction.timeRange = CMTimeRangeMake(firstVideoAssetTrack.timeRange.duration, CMTimeAdd(firstVideoAssetTrack.timeRange.duration, secondVideoAssetTrack.timeRange.duration));
// Create the second layer instruction and associate it with the composition video track.
AVMutableVideoCompositionLayerInstruction *secondVideoLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:mutableCompositionVideoTrack];
// Attach the first layer instruction to the first video composition instruction.
firstVideoCompositionInstruction.layerInstructions = @[firstVideoLayerInstruction];
// Attach the second layer instruction to the second video composition instruction.
secondVideoCompositionInstruction.layerInstructions = @[secondVideoLayerInstruction];
// Attach both of the video composition instructions to the video composition.
AVMutableVideoComposition *mutableVideoComposition = [AVMutableVideoComposition videoComposition];
mutableVideoComposition.instructions = @[firstVideoCompositionInstruction, secondVideoCompositionInstruction];
Incorporating Core Animation Effects
A video composition can add the power of Core Animation to your composition through the animationTool
property. Through this animation tool, you can accomplish tasks such as watermarking video and adding titles or animating overlays. Core Animation can be used in two different ways with video compositions: You can add a Core Animation layer as its own individual composition track, or you can render Core Animation effects (using a Core Animation layer) into the video frames in your composition directly. The following code displays the latter option by adding a watermark to the center of the video:
CALayer *watermarkLayer = <#CALayer representing your desired watermark image#>;
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, mutableVideoComposition.renderSize.width, mutableVideoComposition.renderSize.height);
videoLayer.frame = CGRectMake(0, 0, mutableVideoComposition.renderSize.width, mutableVideoComposition.renderSize.height);
[parentLayer addSublayer:videoLayer];
watermarkLayer.position = CGPointMake(mutableVideoComposition.renderSize.width/2, mutableVideoComposition.renderSize.height/4);
[parentLayer addSublayer:watermarkLayer];
mutableVideoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
組合多個 Multiple Assets 并保存到相冊完整示例：
實現(xiàn)思路：
- Create an AVMutableComposition object and add multiple AVMutableCompositionTrack objects
- Add time ranges of AVAssetTrack
objects to compatible composition tracks - Check the preferredTransform property of a video asset track to determine the video’s orientation
- Use AVMutableVideoCompositionLayerInstruction objects to apply transforms to the video tracks within a composition
- Set appropriate values for the renderSize
and frameDuration properties of a video composition - Use a composition in conjunction with a video composition when exporting to a video file
- Save a video file to the Camera Roll
Note: To focus on the most relevant code, this example omits several aspects of a complete app, such as memory management and error handling. To use AVFoundation, you are expected to have enough experience with Cocoa to infer the missing pieces.
Creating the Composition
AVMutableComposition *mutableComposition = [AVMutableComposition composition];
AVMutableCompositionTrack *videoCompositionTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack *audioCompositionTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
Adding the Assets
AVAssetTrack *firstVideoAssetTrack = [[firstVideoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
AVAssetTrack *secondVideoAssetTrack = [[secondVideoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
[videoCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, firstVideoAssetTrack.timeRange.duration) ofTrack:firstVideoAssetTrack atTime:kCMTimeZero error:nil];
[videoCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, secondVideoAssetTrack.timeRange.duration) ofTrack:secondVideoAssetTrack atTime:firstVideoAssetTrack.timeRange.duration error:nil];
[audioCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeAdd(firstVideoAssetTrack.timeRange.duration, secondVideoAssetTrack.timeRange.duration)) ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:nil];
Note: This assumes that you have two assets that contain at least one video track each and a third asset that contains at least one audio track. The videos can be retrieved from the Camera Roll, and the audio track can be retrieved from the music library or the videos themselves.
Checking the Video Orientations
if you try to combine a video shot in portrait mode with a video shot in landscape mode, the export session will fail to complete.
BOOL isFirstVideoPortrait = NO;
CGAffineTransform firstTransform = firstVideoAssetTrack.preferredTransform;
// Check the first video track's preferred transform to determine if it was recorded in portrait mode.
if (firstTransform.a == 0 && firstTransform.d == 0 && (firstTransform.b == 1.0 || firstTransform.b == -1.0) && (firstTransform.c == 1.0 || firstTransform.c == -1.0)) {
isFirstVideoPortrait = YES;
}
BOOL isSecondVideoPortrait = NO;
CGAffineTransform secondTransform = secondVideoAssetTrack.preferredTransform;
// Check the second video track's preferred transform to determine if it was recorded in portrait mode.
if (secondTransform.a == 0 && secondTransform.d == 0 && (secondTransform.b == 1.0 || secondTransform.b == -1.0) && (secondTransform.c == 1.0 || secondTransform.c == -1.0)) {
isSecondVideoPortrait = YES;
}
if ((isFirstVideoAssetPortrait && !isSecondVideoAssetPortrait) || (!isFirstVideoAssetPortrait && isSecondVideoAssetPortrait)) {
UIAlertView *incompatibleVideoOrientationAlert = [[UIAlertView alloc] initWithTitle:@"Error!" message:@"Cannot combine a video shot in portrait mode with a video shot in landscape mode." delegate:self cancelButtonTitle:@"Dismiss" otherButtonTitles:nil];
[incompatibleVideoOrientationAlert show];
return;
}
Applying the Video Composition Layer Instructions
Once you know the video segments have compatible orientations, you can apply the necessary layer instructions to each one and add these layer instructions to the video composition.
AVMutableVideoCompositionInstruction *firstVideoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
// Set the time range of the first instruction to span the duration of the first video track.
firstVideoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, firstVideoAssetTrack.timeRange.duration);
AVMutableVideoCompositionInstruction * secondVideoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
// Set the time range of the second instruction to span the duration of the second video track.
secondVideoCompositionInstruction.timeRange = CMTimeRangeMake(firstVideoAssetTrack.timeRange.duration, CMTimeAdd(firstVideoAssetTrack.timeRange.duration, secondVideoAssetTrack.timeRange.duration));
AVMutableVideoCompositionLayerInstruction *firstVideoLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoCompositionTrack];
// Set the transform of the first layer instruction to the preferred transform of the first video track.
[firstVideoLayerInstruction setTransform:firstTransform atTime:kCMTimeZero];
AVMutableVideoCompositionLayerInstruction *secondVideoLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoCompositionTrack];
// Set the transform of the second layer instruction to the preferred transform of the second video track.
[secondVideoLayerInstruction setTransform:secondTransform atTime:firstVideoAssetTrack.timeRange.duration];
firstVideoCompositionInstruction.layerInstructions = @[firstVideoLayerInstruction];
secondVideoCompositionInstruction.layerInstructions = @[secondVideoLayerInstruction];
AVMutableVideoComposition *mutableVideoComposition = [AVMutableVideoComposition videoComposition];
mutableVideoComposition.instructions = @[firstVideoCompositionInstruction, secondVideoCompositionInstruction];
Setting the Render Size and Frame Duration
CGSize naturalSizeFirst, naturalSizeSecond;
// If the first video asset was shot in portrait mode, then so was the second one if we made it here.
if (isFirstVideoAssetPortrait) {
// Invert the width and height for the video tracks to ensure that they display properly.
naturalSizeFirst = CGSizeMake(firstVideoAssetTrack.naturalSize.height, firstVideoAssetTrack.naturalSize.width);
naturalSizeSecond = CGSizeMake(secondVideoAssetTrack.naturalSize.height, secondVideoAssetTrack.naturalSize.width);
}
else {
// If the videos weren't shot in portrait mode, we can just use their natural sizes.
naturalSizeFirst = firstVideoAssetTrack.naturalSize;
naturalSizeSecond = secondVideoAssetTrack.naturalSize;
}
float renderWidth, renderHeight;
// Set the renderWidth and renderHeight to the max of the two videos widths and heights.
if (naturalSizeFirst.width > naturalSizeSecond.width) {
renderWidth = naturalSizeFirst.width;
}
else {
renderWidth = naturalSizeSecond.width;
}
if (naturalSizeFirst.height > naturalSizeSecond.height) {
renderHeight = naturalSizeFirst.height;
}
else {
renderHeight = naturalSizeSecond.height;
}
mutableVideoComposition.renderSize = CGSizeMake(renderWidth, renderHeight);
// Set the frame duration to an appropriate value (i.e. 30 frames per second for video).
mutableVideoComposition.frameDuration = CMTimeMake(1,30);
Exporting the Composition and Saving it to the Camera Roll
// Create a static date formatter so we only have to initialize it once.
static NSDateFormatter *kDateFormatter;
if (!kDateFormatter) {
kDateFormatter = [[NSDateFormatter alloc] init];
kDateFormatter.dateStyle = NSDateFormatterMediumStyle;
kDateFormatter.timeStyle = NSDateFormatterShortStyle;
}
// Create the export session with the composition and set the preset to the highest quality.
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mutableComposition presetName:AVAssetExportPresetHighestQuality];
// Set the desired output URL for the file created by the export process.
exporter.outputURL = [[[[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:@YES error:nil] URLByAppendingPathComponent:[kDateFormatter stringFromDate:[NSDate date]]] URLByAppendingPathExtension:CFBridgingRelease(UTTypeCopyPreferredTagWithClass((CFStringRef)AVFileTypeQuickTimeMovie, kUTTagClassFilenameExtension))];
// Set the output file type to be a QuickTime movie.
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = mutableVideoComposition;
// Asynchronously export the composition to a video file and save this file to the camera roll once export completes.
[exporter exportAsynchronouslyWithCompletionHandler:^{
dispatch_async(dispatch_get_main_queue(), ^{
if (exporter.status == AVAssetExportSessionStatusCompleted) {
ALAssetsLibrary *assetsLibrary = [[ALAssetsLibrary alloc] init];
if ([assetsLibrary videoAtPathIsCompatibleWithSavedPhotosAlbum:exporter.outputURL]) {
[assetsLibrary writeVideoAtPathToSavedPhotosAlbum:exporter.outputURL completionBlock:NULL];
}
}
});
}];
Exporting the Composition and Saving it to the Camera Roll
// Create a static date formatter so we only have to initialize it once.
static NSDateFormatter *kDateFormatter;
if (!kDateFormatter) {
kDateFormatter = [[NSDateFormatter alloc] init];
kDateFormatter.dateStyle = NSDateFormatterMediumStyle;
kDateFormatter.timeStyle = NSDateFormatterShortStyle;
}
// Create the export session with the composition and set the preset to the highest quality.
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mutableComposition presetName:AVAssetExportPresetHighestQuality];
// Set the desired output URL for the file created by the export process.
exporter.outputURL = [[[[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:@YES error:nil] URLByAppendingPathComponent:[kDateFormatter stringFromDate:[NSDate date]]] URLByAppendingPathExtension:CFBridgingRelease(UTTypeCopyPreferredTagWithClass((CFStringRef)AVFileTypeQuickTimeMovie, kUTTagClassFilenameExtension))];
// Set the output file type to be a QuickTime movie.
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = mutableVideoComposition;
// Asynchronously export the composition to a video file and save this file to the camera roll once export completes.
[exporter exportAsynchronouslyWithCompletionHandler:^{
dispatch_async(dispatch_get_main_queue(), ^{
if (exporter.status == AVAssetExportSessionStatusCompleted) {
ALAssetsLibrary *assetsLibrary = [[ALAssetsLibrary alloc] init];
if ([assetsLibrary videoAtPathIsCompatibleWithSavedPhotosAlbum:exporter.outputURL]) {
[assetsLibrary writeVideoAtPathToSavedPhotosAlbum:exporter.outputURL completionBlock:NULL];
}
}
});
}];
Still and Video Media Capture
To manage the capture from a device such as a camera or microphone, you assemble objects to represent inputs and outputs, and use an instance of AVCaptureSession
to coordinate the data flow between them. Minimally you need:
An instance of AVCaptureDevice
to represent the input device, such as a camera or microphoneAn instance of a concrete subclass of AVCaptureInput
to configure the ports from the input deviceAn instance of a concrete subclass of AVCaptureOutput
to manage the output to a movie file or still imageAn instance of AVCaptureSession
to coordinate the data flow from the input to the output
Time and Media Representations
CMTime Represents a Length of Time
CMTime is a C structure that represents time as a rational number, with a numerator (an int64_t
value), and a denominator (an int32_t
timescale). Conceptually, the timescale specifies the fraction of a second each unit in the numerator occupies. Thus if the timescale is 4, each unit represents a quarter of a second; if the timescale is 10, each unit represents a tenth of a second, and so on. You frequently use a timescale of 600, because this is a multiple of several commonly used frame rates: 24 fps for film, 30 fps for NTSC (used for TV in North America and Japan), and 25 fps for PAL (used for TV in Europe). Using a timescale of 600, you can exactly represent any number of frames in these systems.
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