如何使用 AVAssetExportSession 覆盖 iPhone/iPod 库中的歌曲？

Question

所以据说在 iOS 4 SDK 中你可以编辑并写入用户的 iTunes 库。我可以从 iPhone/iPod 库成功加载 AVAsset，但作为快速测试，我尝试使用 AVAssetExportSession 立即覆盖同一文件，但它总是返回状态“4”，我认为 是 AVAssetExportSessionStatusFailed...在文档中它说：

enum {
    AVAssetExportSessionStatusUnknown,
    AVAssetExportSessionStatusExporting,
    AVAssetExportSessionStatusCompleted,
    AVAssetExportSessionStatusFailed,
    AVAssetExportSessionStatusCancelled,
    AVAssetExportSessionStatusWaiting
};

但在 AVAssetExportSession.h 中它说：

enum {
    AVAssetExportSessionStatusUnknown,
    AVAssetExportSessionStatusWaiting,
    AVAssetExportSessionStatusExporting,
    AVAssetExportSessionStatusCompleted,
    AVAssetExportSessionStatusFailed,
    AVAssetExportSessionStatusCancelled
};
typedef NSInteger AVAssetExportSessionStatus;

这是我正在使用的代码：

// before this, i'm using mpmediapicker to pick an m4a file i synched with my itunes library 

NSURL *assetUrl = [[self.userMediaItemCollection.items objectAtIndex: 0] valueForProperty: MPMediaItemPropertyAssetURL];
AVURLAsset *asset = [AVURLAsset URLAssetWithURL: assetUrl options: nil];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset: asset presetName: AVAssetExportPresetAppleM4A];
exportSession.outputURL = asset.URL;
exportSession.outputFileType = AVFileTypeAppleM4A;

NSLog(@"output filetype: %@", exportSession.outputFileType);
// prints "com.apple.m4a-audio"

[exportSession exportAsynchronouslyWithCompletionHandler: ^(void) {
    NSLog(@"status: %i for %@", exportSession.status, exportSession.outputURL);
    // prints "status: 4 for ipod-library://item/item.m4a?id=3631988601206299774"
}];

[exportSession release];

所以无论哪种方式...我猜它是“失败”或“取消”。以前有其他人成功写入媒体库吗？

谢谢！

Answer 1

您无法写入 itunes 库，现在只能从中读取。

Answer 2

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
NSParameterAssert(library);
if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:[NSURL     fileURLWithPath:movieFileName]]) {
   [library writeVideoAtPathToSavedPhotosAlbum:[NSURL fileURLWithPath:movieFileName]     completionBlock:^(NSURL *assetURL, NSError *error){}];
}
[library release];