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我有一个关于在 AVMutableComposition 中缩放视频长度以加快或减慢速度的问题。我知道这样做的代码是

scaleTimeRange:(CMTimeRange)timeRange toDuration:(CMTime)duration

问题是我不知道如何使用该代码。我目前的作品有一个已录制的视频轨道和一个已提供的音频轨道。

有人可以告诉我如何添加这个来让我的视频轨道加速或减速吗？

这是我的代码：

AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:audioURL options:nil];
AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:videoURL options:nil];    

AVMutableComposition* mixComposition = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionCommentaryTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio 
                                                                                    preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionCommentaryTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) 
                                    ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] 
                                     atTime:kCMTimeZero error:nil];

AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo 
                                                                               preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) 
                               ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] 
                                atTime:kCMTimeZero error:nil];

AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition 
                                                                      presetName:AVAssetExportPresetPassthrough];   

NSString* videoName = @\"export.mov\";

NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:videoName];
NSURL    *exportUrl = [NSURL fileURLWithPath:exportPath];
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