如何使用AVFoundation裁剪视频

Question

我正在尝试使用AVFoundation裁剪我录制的视频.所以我想创建一个AVCaptureVideoPreviewLayer并将帧设置为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截取帧并自己裁剪它们,但我想知道是否有更有效的方法来实现这一点,可能是使用AVExportSession并使用AVVideoComposition.

任何指导将不胜感激.

Answer 1

像这样的东西.99%的代码只是将其设置为自定义CGAffineTransform,然后保存结果.

我假设您希望裁剪的视频占据输出的完整大小/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).

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){}];

Answer 2

ios7添加了一个特定的Layer指令,仅用于裁剪.

videolayerInstruction setCropRectangle:atTime:

_麦克风