关于 iphone:[NSMutableArray objectAtIndex:]: 索引 0 超出 AVURLAsset 中空数组的界限

[NSMutableArray objectAtIndex:]: index 0 beyond bounds for empty array from AVURLAsset

我尝试使用以下代码合并音频。

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AVMutableComposition* composition = [AVMutableComposition composition];
AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:audioURL options:nil];
AVURLAsset* audioAsset1 = [[AVURLAsset alloc]initWithURL:audioURL1 options:nil];
AVURLAsset* audioAsset2 = [[AVURLAsset alloc]initWithURL:audioURL1 options:nil];
AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
NSError* error = NULL;
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,videoAsset.duration)
ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo]objectAtIndex:0]
atTime:kCMTimeZero
AVMutableCompositionTrack *compositionAudioTrack1 = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack1 insertTimeRange:CMTimeRangeMake(kCMTimeZero,audioAsset1.duration)
ofTrack:[[audioAsset1 tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0]
atTime:kCMTimeZero
error:&error];
AVMutableCompositionTrack *compositionAudioTrack2 = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack2 insertTimeRange:CMTimeRangeMake(kCMTimeZero,audioAsset2.duration)
ofTrack:[[audioAsset2 tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0]
atTime:kCMTimeZero
error:&error];

当我尝试执行 "[[audioAsset1 trackingWithMediaType:AVMediaTypeAudio]objectAtIndex:0]" 时，会出现以下错误

1 2	* Terminating app due to uncaught exception 'NSRangeException', reason: '* -[NSMutableArray objectAtIndex:]: index 0 beyond bounds for empty array'

但是当我尝试在控制台中打印 audioAsset1 时，它正在打印 ""。我检查了路径，那个文件在那里。

我的错误是什么？请帮我解决它。