Step 3 is very important. It introduces the time and process to release players: 

- When the user clicks back button, only the `stop` method of the player is called;

    ```objectivec
    
    - (IBAction)onBackButton:(id)sender {
        [self.player stop];
    }
    ```

- After the player sends the `BDCloudMediaPlayerPlaybackDidFinishNotification ` notification, modify the `Playback UI ` from`UINavigationController ` **pop** Drop.  

    ```objectivec
    // Register notifications
    - (void)setupNotifications {
        [[NSNotificationCenter defaultCenter] addObserver:self
        	                                             selector:@selector(onPlayerFinish:)
        	                                                 name:BDCloudMediaPlayerPlaybackDidFinishNotification
        	                                               object:nil];
        	}

        	// Pop after Finish notification
    - (void)onPlayerFinish:(NSNotification*)notification {
        	    // If there are multiple player instances simultaneously, you’d better judge whether the object in the notification is the same as the carried one.
        	    if (notification.object != self.player) {
        	        return;
        	    }
            
        	    // pop UI
        	    [self.navigationController popViewControllerAnimated:YES];
        	}

    ```

This process can ensure that the relevant resources inside the player for this play have been released in case of exiting from ‘play UI’. It is helpful to reuse the player instance to initiate the next play.

- (IBAction)onPlayNext:(id)sender {
    // Stop playing the current video
    [self.player stop];
    
    // Reset the player to the original status.
    [self.player reset];
    
    // Start the initialization and play procedure of the next video. 
    self.player.contentString = @"<next url>";
    self.player.shouldAutoplay = YES;
    [self.player prepareToPlay];
}

Example of codes in the above two steps：  

 - (void)onPlayerPrepared:(NSNotification*)notification {
     // If there are multiple player instances simultaneously, you’d better judge whether the object in the notification is the same as the carried one.
     if (notification.object != self.player) {
         return;
     }
     
     // Get multi-code rate lists.
     NSArray<BDCloudMediaPlayerBitrateItem*>* items = [self.player getSupportedBitrates];
     
     // Display the code rate list on UI.
     [self showBitrateList:items];
 }

 - (IBAction)onChangeBitrate:(id)sender {
     NSInteger index = <bitrateIndex>;
     [self.player setBitrateIndex:index];
 }

 - (void)setMediaInputType:(NSInteger)inputType {
     [self.player setMediaItemsInputType:inputType];
 }

 - (void)onPlayerPrepared:(NSNotification*)notification {
     // If there are multiple player instances simultaneously, you’d better judge whether the object in the notification is the same as the carried one.
     if (notification.object != self.player) {
         return;
     }
     
     // Get multi-code rate lists.
     NSArray* bitrates = [self.player getMediaItems];
     
     // Get the current code rate index 
     int index = (int)[self.player mediaItemIndex];
     
     //  Display the code rate list on UI.
     [self.actions updateBitrateList:bitrates index:index];
 }

 - (void)changeBitrate:(NSInteger)index {
     [self.player setMediaItemIndex:index];
 }

 - (void)setMediaInputType:(NSInteger)inputType {
     [self.player setMediaItemsInputType:inputType];
 }

 - (void)setMediaInputList:(NSArray *)inputList {
     [self.player setMediaItems:inputList];
 }

 - (void)onPlayerPrepared:(NSNotification*)notification {
     // If there are multiple player instances simultaneously, you’d better judge whether the object in the notification is the same as the carried one.
     if (notification.object != self.player) {
         return;
     }
     
     // Get multi-code rate lists.
     NSArray* bitrates = [self.player getMediaItems];
     
     // Get the current code rate index
     int index = (int)[self.player mediaItemIndex];
     
     // Display the code rate list on UI.
     [self.actions updateBitrateList:bitrates index:index];
 }

 - (void)changeBitrate:(NSInteger)index {
     [self.player setMediaItemIndex:index];
 }

- Token mode:

     Set `token` before playing

```objectivec
   (void)play {
       // Set `token` first.
       [self.player setToken:@"<token>"];
       
       // Play the video again.
       self.player.contentString = @"<url>";
       self.player.shouldAutoplay = YES;
       [self.player prepareToPlay];
   }    

NSString* value = @"User-Agent: <your user agent>";
[player setOptionValue:value
                forKey:@"headers"
            ofCategory:BDCloudMediaPlayerOptionCategoryFormat];

    // Start the task
    - (void)taskStart:(BDCloudMediaDownloadTask*)task {
    }

    // Task progress report
    - (void)task:(BDCloudMediaDownloadTask*)task progress:(float)progress { 
        NSLog(@"task%@, download process %.2f", task, progress);
    }

    // The task is complete, and when error is nil, it indicates a successful download.
    - (void)taskEnd:(BDCloudMediaDownloadTask*)task error:(NSError*)error {
        if (!error) {
             NSLog(@"Download succeeded!");
            // Get the local path of the offline video, and offline play can be realized after getting it.
            NSString* path = [task.item.path stringByAppendingPathComponent task.item.index];
        }
    }

When initializing the downloader, the username should be introduced for distinguishing the download and storage of different local login users (if there is no account system in App, a fixed value can be introduced).

    self.downloader = [[BDCloudMediaDownload alloc] initWithUser:@"<user>" delegate:self];

After creating the download task, the task enters the execution pipeline, and the maximum concurrency number of the pipelines is 4. When it exceeds the maximum number of concurrency, the newly created task will be in a state waiting for execution. 

    NSError* error;
    BDCloudMediaDownloadTask* task = [self.downloader downloadTaskWithURL:@"<url>" title:@"<title>" error:&error];

- (void)task:(BDCloudMediaDownloadTask*)task needAuthentication:(NSMutableDictionary*)parameters {
    // When the downloaded video uses PlayerID and PlayerKey encryption mode, you need to set playerID in parameters 
    [parameters setObject:@"<playerId>" forKey:@"playerId"];
    
    // When the video to download uses token encryption method, you need to set token in parameters
    [parameters setObject:@"<token>" forKey:@"token"];
}

// Pause the task
[self.downloader suspendTask:task];

//  resume tasks
[self.downloader resumeTask:task];

self.downloader = [[BDCloudMediaDownload alloc] initWithUser:@"<user>" delegate:self];

// Get the unfinished tasks last time.
self.tasks = [self.downloader resumeUncompletedTasks];

// 1. Initialize CSS sprites rendering configuration and set the essential attributes.
BDCloudSpriteRenderConfiguration *renderConfig = [BDCloudSpriteRenderConfiguration defaultConfiguration];
renderConfig.row = <Number of lines in the thumbnail ofSprite Image>;
renderConfig.column = <The thumbnail Pipeline number in CSS sprites> ;
renderConfig.thumbnailDuration = <Time intervals of every thumbnail>;

// 2. Initialize the CSS sprites download configuration and set the essential attribute.
BDCloudSpriteDownloadConfiguration *downloadConfig = [BDCloudSpriteDownloadConfiguration defaultConfiguration];
downloadConfig.imageList = <CSS sprites URL list>;
downloadConfig.maxThreadNum = <Maximum thread number after downloading>;
downloadConfig.path = <Download link>;

// 3. Initialize CSS sprites rendering control class and add display canvas.
BDCloudSpriteManager *manager = [BDCloudSpriteManager initWithRenderConfig:renderConfig downloadConfig:downloadConfig];
manager.renderView.frame = <Canvas frame>;
[self.view addSubView:manager.renderView]
[manager startDownload:nil];

// 4. After you receive successful callback of downloaded items, display the thumbnail according to the timestamp.
[manager renderTime:<Display the timestamp>]; 

// 1. Pre-download the video. 
[[BDCloudMediaSourceManager sharedInstance] download:url size:downloadSize complete:^(BOOL succ, NSError *error) {
    NSLog(@"pre download succ = %d, error = %@",error);            
}];

// 2. Enable the feature of saving while playing 
[BDCloudMediaSourceManager sharedInstance].autoWriteCache = YES;

// 3. The player is set with network proxy. 
self.player.proxy = [BDCloudMediaSourceManager sharedInstance];

// 4. Start to play after pre-downloading.
[self.player prepareToPlay]；

// 1. Configure basic information of VR playback
// 1.1 Create an information instance by default.
self.vrConfig = [BDCloudVRConfiguration defaultConfig];
// 1.2 Configure VR resource type.
[self.vrConfig setProjectionMode:<projectionMode>];
// 1.3 Configure rendering mode.
[self.vrConfig setDisplayMode:<displayMode>];
// 1.4 Configure the interaction mode. 
[self.vrConfig setInteractiveMode:<interactiveMode>];
// 1.6 Configure pinch gestures. 
[self.vrConfig setPinchEnabled:<pinchEnabled>];

// 2. Receive the decoded information notification, and initialize the VR rendering control class and start VR rendering after configuring the decoding information.
- (void)onPlayerVideoDecoderOpen:(NSNotification *)notification {
    if (notification.object != _player) {
        return;
    }
    if (self.vrConfig) {
        // 2.1 Configure decoding information
        [self.vrConfig setProviderBDCloudMediaPlayerView:_player.view
                               viaHardwareAccelerate:[_player viaHardwareAccelerate]];
        // 2.2 Configuration rendering parent view
        [self.vrConfig setRenderOn:self.player.view];
        // 2.3 Initialize the VR rendering control class
        self.vrManager = [BDCloudVRRenderControl renderWithConfig:self.vrConfig];
        // 2.4 Start VR rendering. 
        [self.vrManager resume];
    }
}