如何使用AVFoundation裁剪视频 [英] How do I use AVFoundation to crop a video

问题描述

我正在尝试使用AVFoundation裁剪我正在录制的视频。因此，假设我创建一个AVCaptureVideoPreviewLayer并将帧设置为300x300。

I'm trying to use AVFoundation to crop videos I'm recording. So lets say i create a AVCaptureVideoPreviewLayer and set the frame to be 300x300.

AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [AVCaptureVideoPreviewLayer     layerWithSession:session];
captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
captureVideoPreviewLayer.delegate = self;
captureVideoPreviewLayer.frame = CGRectMake(0,0, 300, 300);
[previewView.layer addSublayer:captureVideoPreviewLayer];

用户看到视频被裁剪。我想完全按照用户查看的方式保存视频。使用AVCaptureMovieFileOutput，视频显然可以保存而不会裁剪。我正在考虑使用AVCaptureVideoDataOutput拦截帧并自己裁剪它们，但我想知道是否有更有效的方法来执行此操作，可能使用AVExportSession并使用AVVideoComposition。

The user sees the video cropped. I'd like to save the video exactly the way the user is viewing it. Using AVCaptureMovieFileOutput, the video obviously gets saved without cropping. I was considering using a AVCaptureVideoDataOutput to intercept the frames and crop them myself, but I was wondering if there is a more efficient way to do this, perhaps with AVExportSession and using an AVVideoComposition.

任何指导都将不胜感激。

Any guidance would be appreciated.

推荐答案

这样的事情。 99％的代码只是将其设置为自定义CGAffineTransform，然后保存结果。

Soemthing like this. 99% of this code just sets it up to do a custom CGAffineTransform, and then save out the result.

我假设您希望裁剪的视频占用输出的全尺寸/宽度 - 例如，缩放仿射是正确的解决方案（放大视频，产生裁剪+调整大小的效果）。

I'm assuming that you want the cropped video to take up full size/width of the output - so that e.g a Scale Affine is the correct solution (you zoom in on the video, giving the effect of having cropped + resized).

AVAsset* asset = // your input

AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

AVMutableVideoComposition* videoComposition = [[AVMutableVideoComposition videoComposition]retain];
videoComposition.renderSize = CGSizeMake(320, 240);
videoComposition.frameDuration = CMTimeMake(1, 30);

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

AVMutableVideoCompositionLayerInstruction* transformer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];
CGAffineTransform finalTransform = // setup a transform that grows the video, effectively causing a crop
    [transformer setTransform:finalTransform atTime:kCMTimeZero];
    instruction.layerInstructions = [NSArray arrayWithObject:transformer];
videoComposition.instructions = [NSArray arrayWithObject: instruction];

exporter = [[AVAssetExportSession alloc] initWithAsset:saveComposition presetName:AVAssetExportPresetHighestQuality] ;
exporter.videoComposition = videoComposition;
exporter.outputURL=url3;
exporter.outputFileType=AVFileTypeQuickTimeMovie;

[exporter exportAsynchronouslyWithCompletionHandler:^(void){}];

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