如何从iOS上的音频文件中提取元数据

问题描述

我正在尝试使用AVFoundation框架从mp3和m4a文件中提取元数据。

I'm trying to extract metadata from mp3 and m4a files using the AVFoundation framework.

这是测试代码：

+ (void)printMetadataForFileAtPath:(NSString *)path
{
    NSURL *url = [NSURL fileURLWithPath:path];
    AVAsset *asset = [AVURLAsset assetWithURL:url];
    NSArray *availableFormats = [asset availableMetadataFormats];
    NSLog(@"Available formats: %@", availableFormats);
    NSArray *iTunesMetadata = [asset metadataForFormat:AVMetadataFormatiTunesMetadata];
    for (AVMetadataItem *item in iTunesMetadata)
    {
        NSLog(@"%@ %x", item.key, [(NSNumber *)item.key integerValue]);

        if ([item.key isEqual:AVMetadataiTunesMetadataKeySongName])
        {
            NSLog(@"FOUND song name: %@", item.stringValue);
        }
    }
    NSLog(@"====================");
    NSLog(@"%@ %@ %@", AVMetadataiTunesMetadataKeySongName, AVMetadataiTunesMetadataKeyAlbum, AVMetadataiTunesMetadataKeyArtist);
}

这是输出：

Available formats: (
    "com.apple.itunes",
    "com.apple.quicktime.udta"
)
-1452383891 a96e616d
-1455336876 a9415254
1631670868 61415254
-1451789708 a9777274
-1453233054 a9616c62
-1452838288 a9677270
-1452841618 a967656e
1953655662 74726b6e
1684632427 6469736b
-1453039239 a9646179
-1453101708 a9636d74
1668311404 6370696c
1885823344 70676170
1953329263 746d706f
-1451987089 a9746f6f
com.apple.iTunes.iTun
com.apple.iTunes.Enco
1668249202 636f7672
-1452508814 a96c7972
====================
@nam @alb @ART

当解释为4个ASCII字符时：

When interpreted as 4 ASCII chars:

© n a m
© A R T
a A R T
© w r t
© a l b
© g r p
© g e n
t r k n
d i s k
© d a y
© c m t
c p i l
p g a p
t m p o
© t o o

所以似乎 item.key 是 NSNumber 对象，但以 AVMetadataiTunesMetadataKey ... 开头的常量是 NSString 对象。获取元数据的正确方法是什么？当我使用 [AVAsset commonMetadata] 时，键也是 NSString 对象以及与的比较AVMetadataCommonKey ... 常量按预期工作。

So it seems that item.key is a NSNumber object but the constants beginning with AVMetadataiTunesMetadataKey... are NSString objects. What's the right way to get the metadata? When i use [AVAsset commonMetadata] the keys are NSString objects too and the comparison with the AVMetadataCommonKey... constants works as expected.

推荐答案

AVFoundation API在处理元数据时非常混乱。

AVFoundation API is quite confusing when dealing with metadata.

AVMetadataiTunesMetadataKey * 定义的键与AVMetadataItem的键属性值不同。 AVMetadataiTunesMetadataKey *键将与 [AVMetadataItem metadataItemsFromArray：withKey：keySpace：AVMetadataKeySpaceiTunes] API一起使用，以使用特定的iTunes密钥过滤掉元数据项。

The keys defined by AVMetadataiTunesMetadataKey* values are not the same ones as AVMetadataItem's key property values. AVMetadataiTunesMetadataKey* keys are to be used with the [AVMetadataItem metadataItemsFromArray:withKey:keySpace:AVMetadataKeySpaceiTunes] API to filter out metadata items with the specific iTunes keys.

AVMetadataItem的键和值取决于资源文件的确切格式。除了使用上述函数过滤掉键外，我建议使用item的 commonKey 属性，该属性提供比其他属性更通用的key属性。

The keys and values for AVMetadataItem depend on the exact format of the resource file. In addition to filtering out the keys with the function above, I suggest using item's commonKey property, which provides more generic "key" property than the others.

更改示例代码以打印 commonKey 以及项目的值。
以下是一些示例：

Change your sample code to print out commonKey along with the item's value.Here are some examples:

• commonKey 是title - value 是一首带有歌曲标题的NSString


• commonKey 是'艺术家' - 值是一个NSString，其艺术家是歌曲


• commonKey 是'albumName' - 值是一张带有专辑名称的NSString

• commonKey is "title" - value is a NSString with the title of the song
• commonKey is 'artist' - value is a NSString with the artist of the song
• commonKey is 'albumName' - value is a NSString with the name of the album

希望这会有所帮助！

这篇关于如何从iOS上的音频文件中提取元数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！