如何检查MPMediaItem的MPMediaType只是音频？ [英] How do I check an MPMediaItem for MPMediaType of just audio?

问题描述

我希望我需要进行逐位比较，但我不清楚如何在Objective-C语法中完成。 MPMediaType的枚举定义如下。

I expect I need to do a bitwise comparison but I am unclear on how that is done in Objective-C syntax. The enum definition of MPMediaType is below.

我需要做的是确保MPMediaItem根本不是视频，因为AVAssetReader会阻塞视频文件，尽管我用MPMediaTypeAnyAudio过滤掉了媒体查询。

What I need to do is ensure the MPMediaItem is not video at all because AVAssetReader is choking on video files despite filtering to MPMediaTypeAnyAudio with my media query.

如何确保MPMediaItem是唯一的音频类型之一？

How can I ensure the MPMediaItem is one of the only audio types?

enum {
    // audio
    MPMediaTypeMusic        = 1 << 0,
    MPMediaTypePodcast      = 1 << 1,
    MPMediaTypeAudioBook    = 1 << 2,
    MPMediaTypeAudioITunesU = 1 << 3, // available in iOS 5.0
    MPMediaTypeAnyAudio     = 0x00ff,

    // video (available in iOS 5.0)
    MPMediaTypeMovie        = 1 << 8,
    MPMediaTypeTVShow       = 1 << 9,
    MPMediaTypeVideoPodcast = 1 << 10,
    MPMediaTypeMusicVideo   = 1 << 11,
    MPMediaTypeVideoITunesU = 1 << 12,
    MPMediaTypeAnyVideo     = 0xff00,

    MPMediaTypeAny          = ~0
};
typedef NSInteger MPMediaType;

推荐答案

要从音乐库中检索所有音乐曲目，尝试：

To retrieve all the music tracks from the music library, try:

MPMediaPropertyPredicate *predicate = [MPMediaPropertyPredicate predicateWithValue:[NSNumber numberWithInteger:MPMediaTypeMusic] forProperty:MPMediaItemPropertyMediaType];

MPMediaQuery *query = [[MPMediaQuery alloc] init];
[query addFilterPredicate:predicate];

NSArray *items = [query items];

检索音乐，有声读物和播客：

To retrieve music, audio books and podcasts:

MPMediaPropertyPredicate *predicate = [MPMediaPropertyPredicate predicateWithValue [NSNumber numberWithInteger:MPMediaTypeMusic | MPMediaTypePodcast | MPMediaTypeAudioBook] forProperty:MPMediaItemPropertyMediaType comparisonType:MPMediaPredicateComparisonContains];

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