iOS 6问题：将MPMediaItem转换为NSData

Question

我已经尝试了下面的代码。

   -(void)mediaItemToData : (MPMediaItem * ) curItem
{
    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";

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString * myDocumentsDirectory = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;

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

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

    // do the export
    // (completion handler block omitted)
    [exporter exportAsynchronouslyWithCompletionHandler:
     ^{
         NSData *data = [NSData dataWithContentsOfFile: [myDocumentsDirectory
                                                         stringByAppendingPathComponent: @"exported.mp4"]];

         DLog(@"Data %@",data);
     }];
}

这段代码在iOS 5中运行良好，但在iOS 6中无法正常工作。

在AVAssetExportPresetPassthrough方面，iOS6有任何变化吗？

- Hitarth

---

看一下这个链接，不确定是否有帮助：http://www.subfurther.com/blog/2010/07/19/from-iphone-media-library-to-pcm-samples-in-dozens-of-confounding-potentially-lossy-steps/ - Leena

@Leena 谢谢你的链接，对解决这个问题很有帮助。 - Hitarth

Answer 1

我已经找到了iOS 6的解决方案。请看下面修改的代码。

-(void)mediaItemToData : (MPMediaItem * ) curItem
{
    NSURL *url = [curItem valueForProperty: MPMediaItemPropertyAssetURL];

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

    AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset: songAsset
                                                                      presetName:AVAssetExportPresetAppleM4A];

    exporter.outputFileType =   @"com.apple.m4a-audio";

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString * myDocumentsDirectory = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;

    [[NSDate date] timeIntervalSince1970];
    NSTimeInterval seconds = [[NSDate date] timeIntervalSince1970];
    NSString *intervalSeconds = [NSString stringWithFormat:@"%0.0f",seconds];

    NSString * fileName = [NSString stringWithFormat:@"%@.m4a",intervalSeconds];

    NSString *exportFile = [myDocumentsDirectory stringByAppendingPathComponent:fileName];

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

    // do the export
    // (completion handler block omitted)
    [exporter exportAsynchronouslyWithCompletionHandler:
     ^{
         int exportStatus = exporter.status;

         switch (exportStatus)
         {
             case AVAssetExportSessionStatusFailed:
             {
                 NSError *exportError = exporter.error;
                 NSLog (@"AVAssetExportSessionStatusFailed: %@", exportError);
                 break;
             }
             case AVAssetExportSessionStatusCompleted:
             {
                 NSLog (@"AVAssetExportSessionStatusCompleted");

                 NSData *data = [NSData dataWithContentsOfFile: [myDocumentsDirectory
                                                                 stringByAppendingPathComponent:fileName]];

                 //DLog(@"Data %@",data);
                 data = nil;

                 break;
             }
             case AVAssetExportSessionStatusUnknown:
             {
                 NSLog (@"AVAssetExportSessionStatusUnknown"); break;
             }
             case AVAssetExportSessionStatusExporting:
             {
                 NSLog (@"AVAssetExportSessionStatusExporting"); break;
             }
             case AVAssetExportSessionStatusCancelled:
             {
                 NSLog (@"AVAssetExportSessionStatusCancelled"); break;
             }
             case AVAssetExportSessionStatusWaiting:
             {
                 NSLog (@"AVAssetExportSessionStatusWaiting"); break;
             }
             default:
             {
                 NSLog (@"didn't get export status"); break;
             }
         }
     }];
}

请查看 此链接 获取更多信息。

- Hitarth

Answer 2

尝试使用Swift4编写的AVAssetExportSession，原因是https://stackoverflow.com/a/36694392/5653015

func mediaPicker(_ mediaPicker: MPMediaPickerController, didPickMediaItems mediaItemCollection: MPMediaItemCollection)
{
    //get media item first
    guard let mediaItem = mediaItemCollection.items.first else
    {
        NSLog("No item selected.")
        return
    }


    let songUrl = mediaItem.value(forProperty: MPMediaItemPropertyAssetURL) as! URL
    print(songUrl)

    // get file extension andmime type
    let str = songUrl.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: "")

    let exportSession = AVAssetExportSession(asset: AVAsset(url: songUrl), presetName: AVAssetExportPresetAppleM4A)
    exportSession?.shouldOptimizeForNetworkUse = true
    exportSession?.outputFileType = AVFileType.m4a

    //save it into your local directory
    let documentURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
    let outputURL = documentURL.appendingPathComponent(mediaItem.title!)
    print(outputURL.absoluteString)
    //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")
          //  self.getAudio()
        }
        self.dismiss(animated: true, completion: nil)
    })
}

- iOS Lifee

Answer 3

SWIFT 3版本来自@Hitarth

func save(mediaItem: MPMediaItem) -> String? {
    let url = mediaItem.assetURL!
    let hex = MD5Hex(string: url.absoluteString)
    guard didMD5HexExist(string: hex) == false else {
        return hex
    }
    let songAsset = AVURLAsset(url: url)
    guard let exporter = AVAssetExportSession(asset: songAsset, presetName: AVAssetExportPresetAppleM4A) else {
        assertionFailure()
        return nil
    }
    exporter.outputFileType = "com.apple.m4a-audio"

    let fileHexName = hex + ".m4a"
    let fileURL = latFileManager.getResourceFolderPath().appendingPathComponent(fileHexName)
    DLog("fileURL: \(fileURL)")

    exporter.outputURL = fileURL
    // do the export
    exporter.exportAsynchronously {
        let status = exporter.status
        switch status {
        case .failed:
            assertionFailure(exporter.error as! String)
        case .completed:
            DLog("AVAssetExportSessionStatusCompleted")
            self.fileHexArray.append(fileHexName)
        default:
            DLog("default")
            break
        }
    }
    return hex
}

- Jerome