AVFoundation 框架初探究（四）

 

 

叨叨兩句

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      動手寫這篇總結時候也是二月底過完年回來上班了，又開始新的一年了，今年會是什麼樣子？這問題可能得年末再回答本身了。在家窩了那麼久，上班仍是的接着看咱們要看的東西，畢竟咱們要作的事還真的太多的。

      總結第五章的內容，這兩天把後面幾章的內容大概的翻着看了看，知道了下後面幾章的內容大體講的都是那些內容。這裏就先開始總結書本中第五章的內容。前面第四章的內容視頻播放咱們再前面的確也總過了，就不在這裏再去重複總結。

   

一：AVPlayerViewController

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      在第五章的最開始講述的就是AVPlayerViewController，這個控制器在前面也沒有好好說過，不過蘋果給咱們的關於AVPlayerViewController的API也就那麼多，咱們在這裏看看它的頭文件，以及它的一些使用。下面就先看看AVPlayerViewController這個類的頭文件的方法，咱們對它的屬性進行一個解釋說明：

File:  AVPlayerViewController.h
Framework:  AVKit
Copyright © 2014-2017 Apple Inc. All rights reserved.
導入庫頭文件
#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>

NS_ASSUME_NONNULL_BEGIN
//AVPlayerViewController有這個代理，這個代理方法就在下面
@protocol AVPlayerViewControllerDelegate;

@class           AVPlayerViewController
這個摘要說明了AVPlayerViewController這個控制器的基本特徵
@abstract        AVPlayerViewController is a subclass of UIViewController that can be used to display the visual content of an AVPlayer object and the standard playback controls.

// 8.0以後有的AVPlayerViewController
API_AVAILABLE(ios(8.0))
@interface AVPlayerViewController : UIViewController
 
// 簡單的播放器AVPlayer屬性
@property        player
@abstract        The player from which to source the media content for the view controller.
@property (nonatomic, strong, nullable) AVPlayer *player;

// 是否展現添加在上面的子控件
@property        showsPlaybackControls
@abstract        Whether or not the receiver shows playback controls. Default is YES.
@discussion        Clients can set this property to NO when they don't want to have any playback controls on top of the visual content (e.g. for a game splash screen).
@property (nonatomic) BOOL showsPlaybackControls;

// 這個屬性字面意思是視頻重力  其實它是用來肯定在承載層的範圍內視頻能夠拉伸或者縮放的程度
// 具體的在下面@discussion部分有討論，咱們再總結一下它三個值分別表明的含義
// AVLayerVideoGravityResizeAspect 會在承載層的範圍內縮放視頻的大小來保持視頻的原始比例寬高，默認值
// AVLayerVideoGravityResizeAspectFill 保留視頻的寬高比，而且經過縮放填滿整個播放界面
// AVLayerVideoGravityResize 會將視頻內容拉伸匹配承載層的範圍，通常不經常使用，由於會把圖片扭曲致使變形
@property        videoGravity
@abstract        A string defining how the video is displayed within an AVPlayerLayer bounds rect.
@discussion      Options are AVLayerVideoGravityResizeAspect, AVLayerVideoGravityResizeAspectFill and AVLayerVideoGravityResize. AVLayerVideoGravityResizeAspect is default.
 See <AVFoundation/AVAnimation.h> for a description of these options.
@property (nonatomic, copy) NSString *videoGravity;

// 經過這個bool類型的值肯定視頻是否已經準備好展現
@property        readyForDisplay
@abstract        Boolean indicating that the first video frame has been made ready for display for the current item of the associated AVPlayer.
@property (nonatomic, readonly, getter = isReadyForDisplay) BOOL readyForDisplay;

// 視頻的尺寸
@property        videoBounds
@abstract        The current size and position of the video image as displayed within the receiver's view's bounds.
@property (nonatomic, readonly) CGRect videoBounds;

// 有自定義的控件能夠添加在這裏UIView上
@property        contentOverlayView
@abstract        Use the content overlay view to add additional custom views between the video content and the controls.
@property (nonatomic, readonly, nullable) UIView *contentOverlayView;

// 是否容許使用畫中畫播放模式，這個畫中畫播放在下面會寫Demo  9.0以後的屬性
@property        allowsPictureInPicturePlayback
@abstract        Whether or not the receiver allows Picture in Picture playback. Default is YES.
@property (nonatomic) BOOL allowsPictureInPicturePlayback API_AVAILABLE(ios(9.0));

// 10.0以後的屬性
@property        updatesNowPlayingInfoCenter
@abstract        Whether or not the now playing info center should be updated. Default is YES.
@property (nonatomic) BOOL updatesNowPlayingInfoCenter API_AVAILABLE(ios(10.0));

// 理解摘要的意思是是否容許點擊播放以後自動全屏播放視頻  默認值是NO
@property        entersFullScreenWhenPlaybackBegins
@abstract        Whether or not the receiver automatically enters full screen when the play button is tapped. Default is NO.
@discussion      If YES, the receiver will show a user interface tailored to this behavior.
@property (nonatomic) BOOL entersFullScreenWhenPlaybackBegins API_AVAILABLE(ios(11.0));

// 也是理解摘要，是否容許退出全屏播放在播放結束以後
@property        exitsFullScreenWhenPlaybackEnds
@abstract        Whether or not the receiver automatically exits full screen when playback ends. Default is NO.
@discussion      If multiple player items have been enqueued, the receiver exits fullscreen once no more items are remaining in the queue.
@property (nonatomic) BOOL exitsFullScreenWhenPlaybackEnds API_AVAILABLE(ios(11.0));

// AVPlayerViewControllerDelegate代理
@property        delegate
@abstract        The receiver's delegate.
@property (nonatomic, weak, nullable) id <AVPlayerViewControllerDelegate> delegate API_AVAILABLE(ios(9.0));
@end

// 下面就是AVPlayerViewControllerDelegate代理方法  下面的代理方法都是optional可選的
@protocol        AVPlayerViewControllerDelegate
@abstract        A protocol for delegates of AVPlayerViewController.
@protocol AVPlayerViewControllerDelegate <NSObject>
@optional

@method          playerViewControllerWillStartPictureInPicture:
@param           playerViewController The player view controller.
@abstract        Delegate can implement this method to be notified when Picture in Picture will start.
// 即將開始畫中畫播放
- (void)playerViewControllerWillStartPictureInPicture:(AVPlayerViewController *)playerViewController;

@method          playerViewControllerDidStartPictureInPicture:
@param           playerViewController  The player view controller.
@abstract        Delegate can implement this method to be notified when Picture in Picture did start.
// 已經開始了畫中畫播放模式
- (void)playerViewControllerDidStartPictureInPicture:(AVPlayerViewController *)playerViewController;

@method          playerViewController:failedToStartPictureInPictureWithError:
@param           playerViewController  The player view controller.
@param           error An error describing why it failed.
@abstract        Delegate can implement this method to be notified when Picture in Picture failed to start.
// 這個摘要已經給咱們說的比較清楚了，當畫中畫模式播放失敗以後就會走這個代理方法
- (void)playerViewController:(AVPlayerViewController *)playerViewController failedToStartPictureInPictureWithError:(NSError *)error;

@method          playerViewControllerWillStopPictureInPicture:
@param           playerViewController The player view controller.
@abstract        Delegate can implement this method to be notified when Picture in Picture will stop.
// 畫中畫播放模式即將結束
- (void)playerViewControllerWillStopPictureInPicture:(AVPlayerViewController *)playerViewController;

@method          playerViewControllerDidStopPictureInPicture:
@param           playerViewController  The player view controller.
@abstract        Delegate can implement this method to be notified when Picture in Picture did stop.
// 畫中畫播放已經結束
- (void)playerViewControllerDidStopPictureInPicture:(AVPlayerViewController *)playerViewController;

@method          playerViewControllerShouldAutomaticallyDismissAtPictureInPictureStart:
@param           playerViewController   The player view controller.
@abstract        Delegate can implement this method and return NO to prevent（阻止） player view controller from automatically being dismissed when Picture in Picture starts.
// 要是在畫中畫開始播放的時候 播放的底層控制器要是消失就返回NO
- (BOOL)playerViewControllerShouldAutomaticallyDismissAtPictureInPictureStart:(AVPlayerViewController *)playerViewController;

@method          playerViewController:restoreUserInterfaceForPictureInPictureStopWithCompletionHandler:
@param           playerViewController  The player view controller.
@param           completionHandler  The completion handler the delegate needs to call after restore.
@abstract        Delegate can implement this method to restore（恢復） the user interface（交互） before Picture in Picture stops.
//  畫中畫播放結束恢復用戶交互
- (void)playerViewController:(AVPlayerViewController *)playerViewController restoreUserInterfaceForPictureInPictureStopWithCompletionHandler:(void (^)(BOOL restored))completionHandler;

@end
NS_ASSUME_NONNULL_END

 

 

就這兩點了

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      書中的第四五章的內容在總結也就還剩這麼兩點，因爲還有部分涉及到的是Mac OS 系統的部分知識，咱們就在這裏不提了，就說說還須要咱們理解的兩點：

 

      一： CMTime  也是對第四章一點內容的補充

             咱們簡單的看看這個CMTime的通常算數運算

#pragma mark --
#pragma mark -- CMTime的簡單的使用
-(void)CMTimeCalculate{
        
        CMTime timeO = CMTimeMake(1,10);
        CMTime timeT = CMTimeMake(1,5);
        
        // 加
        CMTime timeA = CMTimeAdd(timeO,timeT);
        CMTimeShow(timeA);
        
        //減
        CMTime timeS = CMTimeSubtract(timeO,timeT);
        CMTimeShow(timeS);
        
        //乘 整形
        CMTime timeB = CMTimeMake(1,10);
        CMTime timeI = CMTimeMultiply(timeB,5);
        CMTimeShow(timeI);
        
        //乘 浮點型
        CMTime timeF = CMTimeMultiplyByFloat64(timeB,5.6);
        CMTimeShow(timeF);
        
        // 比較  1是大於  0是相等  -1是小於
        int timeC = CMTimeCompare(timeO,timeT);
        NSLog(@"比較獲得大的是%d",timeC); // -1
        
        //求絕對值
        CMTime timeAB = CMTimeAbsoluteValue(timeS);
        CMTimeShow(timeAB);
}

 

      CMTimeRange也是屬於CMTime範疇，下面是在咱們的iOS源代碼對於它的定義：

/*!
	@typedef	CMTimeRange
	@abstract	A time range represented as two CMTime structures.
*/
typedef struct
{
	CMTime			start;		/*! @field start The start time of the time range. */
	CMTime			duration;	/*! @field duration The duration of the time range. */
} CMTimeRange;

      經過這個定義咱們就瞭解了它的組成，在Demo中咱們已是簡單的使用過它了，具體點的咱們能夠在代碼中去查看。

      關於CMTime還有一點值得咱們注意,那就是它和秒之間的轉換函數： Float64 CMTimeGetSeconds(CMTime time)  經過這個函數，你就能夠把一個CMTime實例轉換成Float64位對象。

 

 

AVAssetExportSession

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      咱們先看看在咱們的Demo裏面咱們使用到的關於AVAssetExportSession的代碼，咱們在這裏使用它的時候只是利用它進行了一下視頻的壓縮：

#pragma mark --
#pragma mark -- 視頻壓縮方法
-(void)compressVideoWithFileUrl:(NSURL *)fileUrl{
    
    /* 
      這裏須要注意的一點就是在重複的路徑上保存文件是不行的，能夠選擇在點擊開始的時候刪除以前的
      也能夠這樣按照時間命名不一樣的文件保存
      在後面的 AVAssetWriter 也要注意這一點
     */
    // 壓縮後的視頻的方法命名
    NSDateFormatter * formatter = [[NSDateFormatter alloc]init];
    [formatter setDateFormat:@"yyyy-MM-dd-HH:mm:ss"];
        
    // 壓縮後的文件路徑
    self.videoPath = [NSString stringWithFormat:@"%@/%@.mov",NSTemporaryDirectory(),[formatter stringFromDate:[NSDate date]]];
    
    // 先根據你傳入的文件的路徑穿件一個AVAsset
    AVAsset * asset = [AVAsset  assetWithURL:fileUrl];
    /*
     
     根據urlAsset建立AVAssetExportSession壓縮類
     第二個參數的意義：經常使用 壓縮中等質量  AVAssetExportPresetMediumQuality
     AVF_EXPORT NSString *const AVAssetExportPresetLowQuality        NS_AVAILABLE_IOS(4_0);
     AVF_EXPORT NSString *const AVAssetExportPresetMediumQuality     NS_AVAILABLE_IOS(4_0);
     AVF_EXPORT NSString *const AVAssetExportPresetHighestQuality    NS_AVAILABLE_IOS(4_0);
    
    */
    AVAssetExportSession * exportSession = [[AVAssetExportSession alloc]initWithAsset:asset presetName:AVAssetExportPresetMediumQuality];
    
    // 優化壓縮，這個屬性能使壓縮的質量更好
    exportSession.shouldOptimizeForNetworkUse = YES;
    // 處處的文件的路徑
    exportSession.outputURL =  [NSURL fileURLWithPath:self.videoPath];
    // 導出的文件格式
    /*!
      @constant  AVFileTypeMPEG4  mp4格式的   AVFileTypeQuickTimeMovie mov格式的
      @abstract A UTI for the MPEG-4 file format.
      @discussion
      The value of this UTI is @"public.mpeg-4".
      Files are identified with the .mp4 extension.
      能夠看看這個outputFileType格式，好比AVFileTypeMPEG4也能夠寫成public.mpeg-4，其餘相似
    */
    exportSession.outputFileType = AVFileTypeQuickTimeMovie;
    
    NSLog(@"視頻壓縮後的presetName: %@",exportSession.presetName);
    // 壓縮的方法  export 導出  Asynchronously 異步
    [exportSession exportAsynchronouslyWithCompletionHandler:^{
        
        /*
         exportSession.status 枚舉屬性
         typedef NS_ENUM(NSInteger, AVAssetExportSessionStatus) {
         AVAssetExportSessionStatusUnknown,
         AVAssetExportSessionStatusWaiting,
         AVAssetExportSessionStatusExporting,
         AVAssetExportSessionStatusCompleted,
         AVAssetExportSessionStatusFailed,
         AVAssetExportSessionStatusCancelled
         };
         */
        int exportStatus = exportSession.status;
        switch (exportStatus) {
            case AVAssetExportSessionStatusFailed:
                
                NSLog(@"壓縮失敗");
                break;
            case AVAssetExportSessionStatusCompleted:
            {
                /*
                 壓縮後的大小
                 也能夠利用exportSession的progress屬性，隨時監測壓縮的進度
                 */
                NSData * data = [NSData dataWithContentsOfFile:self.videoPath];
                float dataSize = (float)data.length/1024/1024;
                NSLog(@"視頻壓縮後大小 %f M", dataSize);
               
            }
                break;
            default:
                break;
        }
    }];
}

 

      總結一下：

      經過補充上面的這兩點就算是總結完了書中前五章大概的內容，經過後面這兩點的學習，能總結出來的就是多看API文件！摘要雖然都是英文的，有些同行可能由於不太好就不會去看，但讀懂一些基本的英文文檔也是咱們的基本技能，經過看API能夠學到許多東西！