设置和获取AVMetadataCommonKeyCreator的值时出现问题

AVAssetWriter

AVAssetWriter *assetWrtr = [[AVAssetWriter alloc] initWithURL:inURL fileType:AVFileTypeQuickTimeMovie error:&error];
self.assetWriter = assetWrtr;
[assetWrtr release];

NSArray *existingMetadataArray = self.assetWriter.metadata;
NSMutableArray *newMetadataArray = nil;
if (existingMetadataArray) 
{
    newMetadataArray = [existingMetadataArray mutableCopy]; // To prevent overriding of existing metadata
}
else 
{
    newMetadataArray = [[NSMutableArray alloc] init];
}

AVMutableMetadataItem *item = [[AVMutableMetadataItem alloc] init];
item.keySpace = AVMetadataKeySpaceCommon;
item.key = AVMetadataCommonKeyCreator;
item.value = @\"My App\";

[newMetadataArray addObject:item];
self.assetWriter.metadata = newMetadataArray;
[newMetadataArray release];
[item release];

NSURL *outputFileURL = [self.assetWriter outputURL];
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:outputFileURL options:nil];
NSArray *keys = [NSArray arrayWithObject:@\"commonMetadata\"];

[asset loadValuesAsynchronouslyForKeys:keys completionHandler:^(void) {

    NSError *error = nil;
    AVKeyValueStatus durationStatus = [asset statusOfValueForKey:@\"commonMetadata\" error:&error];
    switch (durationStatus) {
        case AVKeyValueStatusLoaded:
            NSLog(@\"AVKeyValueStatusLoaded\");
            NSLog(@\"commonMetadata:%@\", [asset commonMetadata]);
            break;
        case AVKeyValueStatusFailed:
            NSLog(@\"AVKeyValueStatusFailed\");
            break;
        case AVKeyValueStatusCancelled:
            NSLog(@\"AVKeyValueStatusCancelled\");
            break;
    }
}];

[asset commonMetadata]

AVMetadataItems

AVMetadataCommonKeyTitle

AVMetadataCommonKeyModel

AVMetadataCommonKeySource

AVMetadataCommonKeyCreator

AVMetadataCommonKeyCreator