将歌曲从 ios 音乐库保存到文档目录

Question

我正在制作一个音乐应用程序，用户可以在其中访问 ios 音乐库并将歌曲保存到其应用程序（即文档目录）。我可以使用 MPMediaPickerController 访问音乐库，但不知道如何处理其委托方法以便将所选歌曲保存到我的文档目录。 目前我正在使用此代码

- (void) mediaPicker: (MPMediaPickerController *) mediaPicker
   didPickMediaItems: (MPMediaItemCollection *) collection
{
    [self dismissViewControllerAnimated:YES completion:nil];
    [self playSelectedMediaCollection: collection];
}


- (void) playSelectedMediaCollection: (MPMediaItemCollection *) collection {

    if (collection.count == 1) {
        NSArray *items = collection.items;
        MPMediaItem *mediaItem =  [items objectAtIndex:0];
        [self mediaItemToData:mediaItem];
    }
}



-(void)mediaItemToData:(MPMediaItem*)mediaItem
{
    // Implement in your project the media item picker

    MPMediaItem *curItem = mediaItem;//musicPlayer.nowPlayingItem;

    NSURL *url = [curItem valueForProperty: MPMediaItemPropertyAssetURL];

    AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL: url options:nil];

    AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset: songAsset
                                                                      presetName: AVAssetExportPresetPassthrough];

    exporter.outputFileType = @"public.mpeg-4";

    NSString *exportFile = [[self myDocumentsDirectory] stringByAppendingPathComponent:
                            @"exported.mp4"];

    NSURL *exportURL = [NSURL fileURLWithPath:exportFile] ;
    exporter.outputURL = exportURL;



    NSData *data = [NSData dataWithContentsOfFile: [[self myDocumentsDirectory]
                                                    stringByAppendingPathComponent: @"exported.mp4"]];
//    
//    NSLog(@"%@",data);
//    NSURL *audioUrl = exportURL;
//    NSLog(@"Audio Url=%@",audioUrl);
//    audioData = [NSData dataWithContentsOfURL:audioUrl];
//    NSLog(@"%@",audioData);
    // Do with data something
    // do the export
    // (completion handler block omitted)
    [exporter exportAsynchronouslyWithCompletionHandler:
     ^{
//         int exportStatus=exporter.status;
         NSLog(@"%d export status",exporter.status);
         if (exporter.status==AVAssetExportSessionStatusCompleted)
         {
             NSLog(@"successfull");
         }
         NSData *data = [NSData dataWithContentsOfFile: [[self myDocumentsDirectory]
                                                         stringByAppendingPathComponent: @"exported.mp4"]];

         NSURL *audioUrl = exportURL;
         NSLog(@"Audio Url=%@",audioUrl);
        audioData = [NSData dataWithContentsOfURL:audioUrl];
         NSLog(@"%@",audioData);
         // Do with data something

     }];
}

在上面的代码中，调试器永远不会来到导出会话异步块。让我知道上述代码中是否需要任何修改，或者您是否有任何工作代码可满足我的要求。 提前谢谢....

Answer 1

我认为是错过了

/

试试这个代码

NSString *exportFile = [[self myDocumentsDirectory] stringByAppendingPathComponent: @"/exported.mp4"];

更新

或者原因可以是您使用的预设名称

/* 此导出选项将导致所有轨道的媒体完全按照存储在源资产中的方式传递到输出，除了 无法通过的轨道，通常是因为指定的 outputFileType 指示的容器格式的限制。 此选项不包含在 -allExportPresets 和 -exportPresetsCompatibleWithAsset 返回的数组中。 */ AVF_EXPORT NSString *const AVAssetExportPresetPassthrough NS_AVAILABLE(10_7, 4_0);

这里是关于 exportAsynchronouslyWithCompletionHandler 的很好的描述：https://developer.apple.com/library/mac/documentation/AVFoundation/Reference/AV‌​AssetExportSession_Class/Reference/Reference.html

Answer 2

对于 Swift 3.0 或 4

func mediaPicker(_ mediaPicker: MPMediaPickerController, didPickMediaItems mediaItemCollection: MPMediaItemCollection) {
    mediaPicker.dismiss(animated: true) {

        print("You selected \(mediaItemCollection)")

        let item: MPMediaItem = mediaItemCollection.items[0]
        let pathURL: URL? = item.value(forProperty: MPMediaItemPropertyAssetURL) as? URL
        if pathURL == nil {
            print("Picking Error")
            return
        }

        // get file extension andmime type
        let str = pathURL!.absoluteString
        let str2 = str.replacingOccurrences( of : "ipod-library://item/item", with: "")
        let arr = str2.components(separatedBy: "?")
        var mimeType = arr[0]
        mimeType = mimeType.replacingOccurrences( of : ".", with: "")

        // Export the ipod library as .m4a file to local directory for remote upload
        let exportSession = AVAssetExportSession(asset: AVAsset(url: pathURL!), presetName: AVAssetExportPresetAppleM4A)
        exportSession?.shouldOptimizeForNetworkUse = true
        exportSession?.outputFileType = AVFileTypeAppleM4A

        let documentURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
        let outputURL = documentURL.appendingPathComponent("custom.m4a")

        //Delete Existing file
        do {
            try FileManager.default.removeItem(at: outputURL)
        } catch let error as NSError {
            print(error.debugDescription)
        }

        exportSession?.outputURL = outputURL
        exportSession?.exportAsynchronously(completionHandler: { () -> Void in

            if exportSession!.status == AVAssetExportSessionStatus.completed  {
                print("Export Successfull")
            }

        })

    }

}