设置和检索AVMetadataCommonKeyCreator的值时出现问题 [英] Issue with setting and retrieving the value of AVMetadataCommonKeyCreator

问题描述

我有一个iPhone视频录制应用程序。我使用 AVAssetWriter 将录制的视频数据写入文件。我也有兴趣将自定义元数据嵌入到文件中。例如：我想将我的应用程序识别为视频的创建者。

I have a video recording app for the iPhone. I am using AVAssetWriter for writing the recorded video data to a file. I am also interested in embedding custom metadata to the file. For eg: I want to identify my application as the creator of the video.

因此在创建资产编写者之后，我使用键<$ c添加创建者值$ c> AVMetadataCommonKeyCreator 到资产作者的元数据。

Hence after creating the asset writer, I am adding the creator value using the key AVMetadataCommonKeyCreator to the metadata of the asset writer.

代码片段如下：

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];

录制完成后，我尝试使用AVURLAsset读取文件内容。

Once the recording is done, I am trying to read the contents of the file using AVURLAsset.

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;
    }
}];

然而 [asset commonMetadata] 未返回任何 AVMetadataItems 。它返回一个空数组。
我能够设置其他元数据对象的值，如 AVMetadataCommonKeyTitle ， AVMetadataCommonKeyModel ， AVMetadataCommonKeySource 。正确检索这些值。问题仅出在 AVMetadataCommonKeyCreator 。请让我知道这种行为的原因。是否无法为 AVMetadataCommonKeyCreator 设置应用特定值？这个键实际上代表了什么？

However [asset commonMetadata] does not return any AVMetadataItems. It returns an empty array. I am able to set the values of other meta data objects like AVMetadataCommonKeyTitle, AVMetadataCommonKeyModel, AVMetadataCommonKeySource. These values are retrieved properly. The problem is only with AVMetadataCommonKeyCreator. Please let me know the reason for this behavior. Is it not possible to set app specific value for AVMetadataCommonKeyCreator? What does this key actually represent?

推荐答案

一年前我遇到了同样的问题。当我使用AVFoundation编写音频文件时，我没有看到任何元数据。我认为AVMetadataCommonKeyCreator不起作用。我现在不能说，但事实并非如此。

I've same problems about one year ago. I didn't see any metadata when I've wrote audio file using AVFoundation. I think that AVMetadataCommonKeyCreator doesn't work. I can't say about now but it was so.

我通过使用C库taglib来解决这个问题 http://taglib.github.com
为iOS构建这个库真的很容易。如果你不能编译它，我想你可以删除一些文件。

I solve this problem by using C library taglib http://taglib.github.com it's really easy to build this library for iOS. I think you can delete some files if you can't compile it.

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