tracksWithMediaType有时会返回0个曲目
在我的应用程序中，我结合了几个.m4a音频文件。 对于组合音频文件，我使用下面的代码。
CMTime nextClipStartTime = kCMTimeZero; AVMutableComposition *composition = [[AVMutableComposition alloc] init]; AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid]; for(NSString * str in filesNamesArray) { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *path = [documentsDirectory stringByAppendingPathComponent:str]; NSURL *url = [[NSURL alloc] initFileURLWithPath:path]; AVAsset *avAsset = [[AVURLAsset alloc] initWithURL:url options:nil]; NSArray *tracks = [avAsset tracksWithMediaType:AVMediaTypeAudio]; if ([tracks count] == 0) { NSLog(@"Tracks = %lu",(unsigned long)[tracks count]); return; } NSLog(@"%@",avAsset); CMTimeRange timeRangeInAsset = CMTimeRangeMake(kCMTimeZero, [avAsset duration]); AVAssetTrack *clipAudioTrack = [[avAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]; ok = [compositionAudioTrack insertTimeRange:timeRangeInAsset ofTrack:clipAudioTrack atTime:nextClipStartTime error:&error]; if (!ok) { NSLog(@"Current Video Track Error: %@",error); } nextClipStartTime = CMTimeAdd(nextClipStartTime, timeRangeInAsset.duration); }
有时’tracksWithMediaType’返回空数组。 为什么会发生这种情况，我们将非常感谢任何帮助。
使用以下命令创建AVAsset时：
AVAsset *avAsset = [[AVURLAsset alloc] initWithURL:url options:nil];
资产必须在准备好使用之前加载其轨道：
[avAsset loadValuesAsynchronouslyForKeys:@"tracks" completionHandler: ^{ AVKeyValueStatus status = [avAsset statusOfValueForKey:@"tracks" error:nil]; if (status == AVKeyValueStatusLoaded) { // Asset is ready now } }];