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我想从我的视频文件中裁剪 CGRect 的指定区域。我遵循了本教程。

我正在使用renderSize属性AVMutableVideoComposition来达到指定的大小。这是我用来将视频裁剪为指定大小的代码。

- (void) cropVideoAtPath:(NSString *) path
{
  //load our movie Asset
  AVAsset *asset = [AVAsset assetWithURL:[NSURL fileURLWithPath:path]];

  //create an avassetrack with our asset
  AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

  //create a video composition and preset some settings
  AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
  videoComposition.frameDuration = CMTimeMake(1, 30);
  //here we are setting its render size to its height x height (Square)

  float deltaHeight = 100;

  videoComposition.renderSize = CGSizeMake(clipVideoTrack.naturalSize.width, clipVideoTrack.naturalSize.height-deltaHeight);

 //create a video instruction
  AVMutableVideoCompositionInstruction *instruction = 
 [AVMutableVideoCompositionInstruction videoCompositionInstruction];
  instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30));

AVMutableVideoCompositionLayerInstruction* transformer [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];

 //    CGAffineTransform t1 = CGAffineTransformMakeTranslation(0, 1000);
 //    CGAffineTransform finalTransform = t1;
 //    [transformer setTransform:finalTransform atTime:kCMTimeZero];

instruction.layerInstructions = [NSArray arrayWithObject:transformer];
videoComposition.instructions = [NSArray arrayWithObject: instruction];

//Create an Export Path to store the cropped video
NSString * documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *exportPathLoc = [documentsPath stringByAppendingFormat:@"/CroppedVideo.mp4"];
NSURL *exportUrl = [NSURL fileURLWithPath:exportPathLoc];

//Remove any prevouis videos at that path
[[NSFileManager defaultManager]  removeItemAtURL:exportUrl error:nil];

//Export
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality] ;
exporter.videoComposition = videoComposition;
exporter.outputURL = exportUrl;
exporter.outputFileType = AVFileTypeQuickTimeMovie;

[exporter exportAsynchronouslyWithCompletionHandler:^
 {
     dispatch_async(dispatch_get_main_queue(), ^{

         NSLog(@"Saved");
         UISaveVideoAtPathToSavedPhotosAlbum([[exporter outputURL] path],nil,nil,nil);

     });
 }];
 }

我的原始视频看起来像这样。图片

我申请后的视频renderSize看起来AVMutableVideoComposition像这样。图片

正如我们所见，底部已成功从原始视频中剪掉。

假设我有一个大小的视频，(1000,1000)我只想要该视频的中心部分(500,500)区域。所以我CGrect会的(0,250,500,500)。在我的情况下，我只想要图像存在的区域，所以我想裁剪顶部栏和底部栏。

所以我申请CGAffineTransform了AVMutableVideoCompositionLayerInstruction这样的

CGAffineTransform t1 = CGAffineTransformMakeTranslation(0, deltaHeight);
CGAffineTransform finalTransform = t1;
[transformer setTransform:finalTransform atTime:kCMTimeZero];

结果如下图所示。

图片

那么如何(x,y)在裁剪视频时应用此值以及我在这里做错了什么。我将不胜感激任何帮助。

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