iOS：合并两个视频，其中一个视频不显示，但正在播放声音

我正在尝试合并两个视频，一个是从youtube下载的，另一个是用UIImagePickerController拍摄的。 合并后，youtube的视频不再显示，而是播放声音。 我猜这个问题是由视频维度之间的差异造成的

这是我的代码，我做错了什么

- (void) MergeVideos {
NSLog(@"start merge");
NSError *avError = nil;
//NSFileManager *fileManager = [NSFileManager defaultManager];

AVMutableComposition *composition = [AVMutableComposition composition];

for (int i = ((int)[videos_arr2 count]-1); i>= 0; i--) {
    AVURLAsset *tmpAsset = [[AVURLAsset alloc] initWithURL:videos_arr2[i] options:nil];

[composition insertTimeRange:CMTimeRangeMake(kCMTimeZero, tmpAsset.duration) ofAsset:tmpAsset atTime:kCMTimeZero error:&avError];
}

AVAssetExportSession *export = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetPassthrough];

export.outputFileType = AVFileTypeMPEG4;

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];

NSFileManager *manager = [NSFileManager defaultManager];

NSString *outputURL = [documentsDirectory stringByAppendingPathComponent:@"movie"] ;
[manager createDirectoryAtPath:outputURL withIntermediateDirectories:YES attributes:nil error:nil];

outputURL = [outputURL stringByAppendingPathComponent:@"movie.mp4"];
[manager removeItemAtPath:outputURL error:nil];

export.outputURL = [NSURL fileURLWithPath:outputURL];

[export exportAsynchronouslyWithCompletionHandler:^(void) {
    player = [[MPMoviePlayerController alloc] initWithContentURL:export.outputURL];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(movieFinishedCallback:)                                                                name:MPMoviePlayerPlaybackDidFinishNotification object:player];
    player.movieSourceType = MPMovieSourceTypeFile;
    [player prepareToPlay];
    player.controlStyle = MPMovieControlStyleNone;
    [player setShouldAutoplay:NO];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(moviePlayerLoadStateChanged:)
                                                 name:MPMoviePlayerLoadStateDidChangeNotification
                                               object:player];
}];

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}

看起来您正在kCMTimeZero处插入两个AVAsset。您应该在上一个资产的持续时间插入下一个资产：

CMTime nextAddTime = kCMTimeZero;
for (int i = ((int)[videos_arr2 count]-1); i>= 0; i--) {
    AVURLAsset *tmpAsset = [[AVURLAsset alloc] initWithURL:videos_arr2[i] options:nil];

[composition insertTimeRange:CMTimeRangeMake(kCMTimeZero, tmpAsset.duration) ofAsset:tmpAsset atTime:nextAddTime error:&avError];
nextAddTime = CMTimeAdd(nextAddTime, tmpAsset.duration);
}

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您是否曾经将MPMovieController推到堆栈上？您还应该确保这两个资源都是本地资源。您还可以尝试使用该功能将视频保存到相册中，以查看它是否在相册中播放。