我正在使用UIImagePickerController捕获视频，我可以使用以下代码裁剪视频，
AVAsset *asset = [AVAsset assetWithURL:url];
//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)
videoComposition.renderSize = CGSizeMake(clipVideoTrack.naturalSize.height, clipVideoTrack.naturalSize.height);
//create a video instruction
AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30));
AVMutableVideoCompositionLayerInstruction* transformer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];
//Here we shift the viewing square up to the TOP of the video so we only see the top
CGAffineTransform t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height, -20);
//Use this code if you want the viewing square to be in the middle of the video
//CGAffineTransform t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height, -(clipVideoTrack.naturalSize.width - clipVideoTrack.naturalSize.height) /2 );
//Make sure the square is portrait
CGAffineTransform t2 = CGAffineTransformRotate(t1, M_PI_2);
CGAffineTransform finalTransform = t2;
[transformer setTransform:finalTransform atTime:kCMTimeZero];
//add the transformer layer instructions, then add to video composition
instruction.layerInstructions = [NSArray arrayWithObject:transformer];
videoComposition.instructions = [NSArray arrayWithObject: instruction];
//Create an Export Path to store the cropped video
NSString *outputPath = [NSString stringWithFormat:@"%@%@", NSTemporaryDirectory(), @"video.mp4"];
NSURL *exportUrl = [NSURL fileURLWithPath:outputPath];
//Remove any prevouis videos at that path
[[NSFileManager defaultManager] removeItemAtURL:exportUrl error:nil];
//Export
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetLowQuality] ;
exporter.videoComposition = videoComposition;
exporter.outputURL = exportUrl;
exporter.outputFileType = AVFileTypeMPEG4;
[exporter exportAsynchronouslyWithCompletionHandler:^
{
dispatch_async(dispatch_get_main_queue(), ^{
//Call when finished
[self exportDidFinish:exporter];
});
}];
但我不知道如何解决方向问题。像instagram和Vine应用程序一样，（即）如果我甚至在横向模式下捕获视频，它应该处于纵向模式并且需要将视频裁剪为方形。请给我解决方案......我正在努力解决这个问题...
答案 0 :(得分：26)
我认为源代码来自此链接（包含项目代码）
http://www.one-dreamer.com/cropping-video-square-like-vine-instagram-xcode/
首先需要了解REAL视频方向：
- (UIImageOrientation)getVideoOrientationFromAsset:(AVAsset *)asset
{
AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
CGSize size = [videoTrack naturalSize];
CGAffineTransform txf = [videoTrack preferredTransform];
if (size.width == txf.tx && size.height == txf.ty)
return UIImageOrientationLeft; //return UIInterfaceOrientationLandscapeLeft;
else if (txf.tx == 0 && txf.ty == 0)
return UIImageOrientationRight; //return UIInterfaceOrientationLandscapeRight;
else if (txf.tx == 0 && txf.ty == size.width)
return UIImageOrientationDown; //return UIInterfaceOrientationPortraitUpsideDown;
else
return UIImageOrientationUp; //return UIInterfaceOrientationPortrait;
}
我以一种方式使该功能返回正确的方向，就好像它是一个图像
然后，我修改了功能以修正正确的方向，支持任何裁剪区域而不仅仅是一个正方形，如下所示：
// apply the crop to passed video asset (set outputUrl to avoid the saving on disk ). Return the exporter session object
- (AVAssetExportSession*)applyCropToVideoWithAsset:(AVAsset*)asset AtRect:(CGRect)cropRect OnTimeRange:(CMTimeRange)cropTimeRange ExportToUrl:(NSURL*)outputUrl ExistingExportSession:(AVAssetExportSession*)exporter WithCompletion:(void(^)(BOOL success, NSError* error, NSURL* videoUrl))completion
{
//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);
CGFloat cropOffX = cropRect.origin.x;
CGFloat cropOffY = cropRect.origin.y;
CGFloat cropWidth = cropRect.size.width;
CGFloat cropHeight = cropRect.size.height;
videoComposition.renderSize = CGSizeMake(cropWidth, cropHeight);
//create a video instruction
AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = cropTimeRange;
AVMutableVideoCompositionLayerInstruction* transformer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];
UIImageOrientation videoOrientation = [self getVideoOrientationFromAsset:asset];
CGAffineTransform t1 = CGAffineTransformIdentity;
CGAffineTransform t2 = CGAffineTransformIdentity;
switch (videoOrientation) {
case UIImageOrientationUp:
t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height - cropOffX, 0 - cropOffY );
t2 = CGAffineTransformRotate(t1, M_PI_2 );
break;
case UIImageOrientationDown:
t1 = CGAffineTransformMakeTranslation(0 - cropOffX, clipVideoTrack.naturalSize.width - cropOffY ); // not fixed width is the real height in upside down
t2 = CGAffineTransformRotate(t1, - M_PI_2 );
break;
case UIImageOrientationRight:
t1 = CGAffineTransformMakeTranslation(0 - cropOffX, 0 - cropOffY );
t2 = CGAffineTransformRotate(t1, 0 );
break;
case UIImageOrientationLeft:
t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.width - cropOffX, clipVideoTrack.naturalSize.height - cropOffY );
t2 = CGAffineTransformRotate(t1, M_PI );
break;
default:
NSLog(@"no supported orientation has been found in this video");
break;
}
CGAffineTransform finalTransform = t2;
[transformer setTransform:finalTransform atTime:kCMTimeZero];
//add the transformer layer instructions, then add to video composition
instruction.layerInstructions = [NSArray arrayWithObject:transformer];
videoComposition.instructions = [NSArray arrayWithObject: instruction];
//Remove any prevouis videos at that path
[[NSFileManager defaultManager] removeItemAtURL:outputUrl error:nil];
if (!exporter){
exporter = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality] ;
}
// assign all instruction for the video processing (in this case the transformation for cropping the video
exporter.videoComposition = videoComposition;
//exporter.outputFileType = AVFileTypeQuickTimeMovie;
if (outputUrl){
exporter.outputURL = outputUrl;
[exporter exportAsynchronouslyWithCompletionHandler:^{
switch ([exporter status]) {
case AVAssetExportSessionStatusFailed:
NSLog(@"crop Export failed: %@", [[exporter error] localizedDescription]);
if (completion){
dispatch_async(dispatch_get_main_queue(), ^{
completion(NO,[exporter error],nil);
});
return;
}
break;
case AVAssetExportSessionStatusCancelled:
NSLog(@"crop Export canceled");
if (completion){
dispatch_async(dispatch_get_main_queue(), ^{
completion(NO,nil,nil);
});
return;
}
break;
default:
break;
}
if (completion){
dispatch_async(dispatch_get_main_queue(), ^{
completion(YES,nil,outputUrl);
});
}
}];
}
return exporter;
}
在正常和前置相机的情况下，以所有录制的视频方向（向上，向下，Lanscape R，风景L）进行测试。我在iPhone 5S（iOS 8.1），iPhone 6 Plus（iOS 8.1）
上进行了测试希望有所帮助
答案 1 :(得分：6)
这是我的代码，用于从磁盘上的视频创建类似藤蔓的视频。这是用swift编写的：
static let MaxDuration: CMTimeValue = 12
class func compressVideoAsset(_ asset: AVAsset, output: URL, completion: @escaping (_ data: Data?) -> Void)
{
let session = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetMediumQuality)!
session.videoComposition = self.squareVideoCompositionForAsset(asset)
session.outputURL = output
session.outputFileType = AVFileTypeMPEG4
session.shouldOptimizeForNetworkUse = true
session.canPerformMultiplePassesOverSourceMediaData = true
let duration = CMTimeValue(CGFloat(asset.duration.value) / CGFloat(asset.duration.timescale) * 30)
session.timeRange = CMTimeRange(start: kCMTimeZero, duration: CMTime(value: min(duration, VideoCompressor.MaxDuration * 30), timescale: 30))
session.exportAsynchronously(completionHandler: { () -> Void in
let data = try? Data(contentsOf: output)
DispatchQueue.main.async(execute: { () -> Void in
completion(data)
})
})
}
private class func squareVideoCompositionForAsset(_ asset: AVAsset) -> AVVideoComposition
{
let track = asset.tracks(withMediaType: AVMediaTypeVideo)[0]
let length = min(track.naturalSize.width, track.naturalSize.height)
var transform = track.preferredTransform
let size = track.naturalSize
let scale: CGFloat = (transform.a == -1 && transform.b == 0 && transform.c == 0 && transform.d == -1) ? -1 : 1 // check for inversion
transform = transform.translatedBy(x: scale * -(size.width - length) / 2, y: scale * -(size.height - length) / 2)
let transformer = AVMutableVideoCompositionLayerInstruction(assetTrack: track)
transformer.setTransform(transform, at: kCMTimeZero)
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRange(start: kCMTimeZero, duration: kCMTimePositiveInfinity)
instruction.layerInstructions = [transformer]
let composition = AVMutableVideoComposition()
composition.frameDuration = CMTime(value: 1, timescale: 30)
composition.renderSize = CGSize(width: length, height: length)
composition.instructions = [instruction]
return composition
}
答案 2 :(得分：5)
我知道这个问题已经过时但有些人可能仍然想知道为什么摄像机中的某些视频会在裁剪后放大。我遇到了这个问题，并意识到我用作帧的cropRect没有根据视频的不同宽高比进行缩放。为了解决这个问题，我只需添加下面的代码即可将视频的顶部裁剪为正方形。如果您想更改位置，只需更改y值，但请务必根据视频进行缩放。 Luca Iaco提供了一些很棒的代码来开始使用。我很感激！
CGSize videoSize = [[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] naturalSize];
float scaleFactor;
if (videoSize.width > videoSize.height) {
scaleFactor = videoSize.height/320;
}
else if (videoSize.width == videoSize.height){
scaleFactor = videoSize.height/320;
}
else{
scaleFactor = videoSize.width/320;
}
CGFloat cropOffX = 0;
CGFloat cropOffY = 0;
CGFloat cropWidth = 320 *scaleFactor;
CGFloat cropHeight = 320 *scaleFactor;