使用 AVFoundation 裁剪 AVAsset 视频 [英] Cropping AVAsset video with AVFoundation
问题描述
我正在使用 AVCaptureMovieFileOutput 录制一些视频.我使用 AVLayerVideoGravityResizeAspectFill 显示预览层，它会稍微放大.我的问题是最终的视频更大，包含在预览期间不适合屏幕的额外图像.
I am using AVCaptureMovieFileOutput to record some video. I have the preview layer displayed using AVLayerVideoGravityResizeAspectFill which zooms in slightly. The problem I have is that the final video is larger, containing extra image that didn't fit on the screen during preview.
这是预览和结果视频
有什么方法可以指定我想使用 AVAssetExportSession 从视频中剪切的 CGRect?
Is there a way I can specify a CGRect that I want to cut from the video using AVAssetExportSession?
编辑----
当我将 CGAffineTransformScale 应用到 AVAssetTrack 时，它会放大视频，并使用 AVMutableVideoComposition renderSize设置为 view.bounds 它会剪掉末端.太好了，只剩下 1 个问题了.视频的宽度没有拉伸到正确的宽度，它只是被黑色填充.
When I apply a CGAffineTransformScale to the AVAssetTrack it zooms into the video, and with the AVMutableVideoComposition renderSize set to view.bounds it crops off the ends. Great, there's just 1 problem left. The width of the video does not stretch to the correct width, it just gets filled with black.
编辑 2 ----建议的问题/答案不完整..
EDIT 2 ---- The suggested question/answer is incomplete..
我的一些代码:
在我的 - (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error 方法我有这个裁剪并调整视频大小.
In my - (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error method I have this to crop and resize the video.
- (void)flipAndSave:(NSURL *)videoURL withCompletionBlock:(void(^)(NSURL *returnURL))completionBlock
{
AVURLAsset *firstAsset = [AVURLAsset assetWithURL:videoURL];
// 1 - Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.
AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];
// 2 - Video track
AVMutableCompositionTrack *firstTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
preferredTrackID:kCMPersistentTrackID_Invalid];
[firstTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, firstAsset.duration)
ofTrack:[[firstAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:nil];
// 2.1 - Create AVMutableVideoCompositionInstruction
AVMutableVideoCompositionInstruction *mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mainInstruction.timeRange = CMTimeRangeMake(CMTimeMakeWithSeconds(0, 600), firstAsset.duration);
// 2.2 - Create an AVMutableVideoCompositionLayerInstruction for the first track
AVMutableVideoCompositionLayerInstruction *firstlayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:firstTrack];
AVAssetTrack *firstAssetTrack = [[firstAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
UIImageOrientation firstAssetOrientation_ = UIImageOrientationUp;
BOOL isFirstAssetPortrait_ = NO;
CGAffineTransform firstTransform = firstAssetTrack.preferredTransform;
if (firstTransform.a == 0 && firstTransform.b == 1.0 && firstTransform.c == -1.0 && firstTransform.d == 0) {
firstAssetOrientation_ = UIImageOrientationRight;
isFirstAssetPortrait_ = YES;
}
if (firstTransform.a == 0 && firstTransform.b == -1.0 && firstTransform.c == 1.0 && firstTransform.d == 0) {
firstAssetOrientation_ = UIImageOrientationLeft;
isFirstAssetPortrait_ = YES;
}
if (firstTransform.a == 1.0 && firstTransform.b == 0 && firstTransform.c == 0 && firstTransform.d == 1.0) {
firstAssetOrientation_ = UIImageOrientationUp;
}
if (firstTransform.a == -1.0 && firstTransform.b == 0 && firstTransform.c == 0 && firstTransform.d == -1.0) {
firstAssetOrientation_ = UIImageOrientationDown;
}
// [firstlayerInstruction setTransform:firstAssetTrack.preferredTransform atTime:kCMTimeZero];
// [firstlayerInstruction setCropRectangle:self.view.bounds atTime:kCMTimeZero];
CGFloat scale = [self getScaleFromAsset:firstAssetTrack];
firstTransform = CGAffineTransformScale(firstTransform, scale, scale);
[firstlayerInstruction setTransform:firstTransform atTime:kCMTimeZero];
// 2.4 - Add instructions
mainInstruction.layerInstructions = [NSArray arrayWithObjects:firstlayerInstruction,nil];
AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition];
mainCompositionInst.instructions = [NSArray arrayWithObject:mainInstruction];
mainCompositionInst.frameDuration = CMTimeMake(1, 30);
// CGSize videoSize = firstAssetTrack.naturalSize;
CGSize videoSize = self.view.bounds.size;
BOOL isPortrait_ = [self isVideoPortrait:firstAsset];
if(isPortrait_) {
videoSize = CGSizeMake(videoSize.height, videoSize.width);
}
NSLog(@"%@", NSStringFromCGSize(videoSize));
mainCompositionInst.renderSize = videoSize;
// 3 - Audio track
AVMutableCompositionTrack *AudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio
preferredTrackID:kCMPersistentTrackID_Invalid];
[AudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, firstAsset.duration)
ofTrack:[[firstAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:nil];
// 4 - Get path
NSString *outputPath = [[NSString alloc] initWithFormat:@"%@%@", NSTemporaryDirectory(), @"cutoutput.mov"];
NSURL *outputURL = [[NSURL alloc] initFileURLWithPath:outputPath];
NSFileManager *manager = [[NSFileManager alloc] init];
if ([manager fileExistsAtPath:outputPath])
{
[manager removeItemAtPath:outputPath error:nil];
}
// 5 - Create exporter
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition
presetName:AVAssetExportPresetHighestQuality];
exporter.outputURL=outputURL;
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = mainCompositionInst;
[exporter exportAsynchronouslyWithCompletionHandler:^{
switch ([exporter status])
{
case AVAssetExportSessionStatusFailed:
NSLog(@"Export failed: %@ : %@", [[exporter error] localizedDescription], [exporter error]);
completionBlock(nil);
break;
case AVAssetExportSessionStatusCancelled:
NSLog(@"Export canceled");
completionBlock(nil);
break;
default: {
NSURL *outputURL = exporter.outputURL;
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock(outputURL);
});
break;
}
}
}];
}
推荐答案
这是我对您问题的解释:您正在屏幕比例为 4:3 的设备上捕获视频，因此您的 AVCaptureVideoPreviewLayer 是 4:3，但视频输入设备以 16:9 捕获视频，因此生成的视频比预览中看到的大".
Here is my interpretation of your question: You are capturing video on a device with a screen ratio of 4:3, thus your AVCaptureVideoPreviewLayer is 4:3, but the video input device captures video in 16:9 so the resulting video is 'larger' than seen in the preview.
如果您只是想裁剪预览未捕获的额外像素，请查看此 http://www.netwalk.be/article/record-square-video-ios.本文展示了如何将视频裁剪成正方形.但是，您只需要进行一些修改即可裁剪为 4:3.我已经去测试了，这是我所做的更改:
If you are simply looking to crop the extra pixels not caught by the preview then check out this http://www.netwalk.be/article/record-square-video-ios. This article shows how to crop the video into a square. However you'll only need a few modifications to crop to 4:3. I've gone and tested this, here are the changes I made:
获得视频的 AVAssetTrack 后，您需要计算新的高度.
Once you have the AVAssetTrack for the video you will need to calculate a new height.
// we convert the captured height i.e. 1080 to a 4:3 screen ratio and get the new height
CGFloat newHeight = clipVideoTrack.naturalSize.height/3*4;
然后修改这两行，使用newHeight.
Then modify these two lines, using newHeight.
videoComposition.renderSize = CGSizeMake(clipVideoTrack.naturalSize.height, newHeight);
CGAffineTransform t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height, -(clipVideoTrack.naturalSize.width - newHeight)/2 );
所以我们在这里所做的是将 renderSize 设置为 4:3 的比例 - 确切的尺寸基于输入设备.然后我们使用 CGAffineTransform 来转换视频位置，这样我们在 AVCaptureVideoPreviewLayer 中看到的就是渲染到我们文件的内容.
So what we've done here is set the renderSize to a 4:3 ratio - the exact dimension are based on the input device. We then use a CGAffineTransform to translate the video position so that what we saw in the AVCaptureVideoPreviewLayer is what is rendered to our file.
编辑:如果您想将所有内容放在一起并根据设备的屏幕比例(3:2、4:3、16:9)裁剪视频并考虑视频方向我们需要添加一些东西.
If you want to put it all together and crop a video based on the device's screen ratio (3:2, 4:3, 16:9) and take the video orientation into mind we need to add a few things.
首先是修改后的示例代码，其中有一些重要的改动:
First here is the modified sample code with a few critical alterations:
// output file
NSString* docFolder = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSString* outputPath = [docFolder stringByAppendingPathComponent:@"output2.mov"];
if ([[NSFileManager defaultManager] fileExistsAtPath:outputPath])
[[NSFileManager defaultManager] removeItemAtPath:outputPath error:nil];
// input file
AVAsset* asset = [AVAsset assetWithURL:outputFileURL];
AVMutableComposition *composition = [AVMutableComposition composition];
[composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
// input clip
AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
// crop clip to screen ratio
UIInterfaceOrientation orientation = [self orientationForTrack:asset];
BOOL isPortrait = (orientation == UIInterfaceOrientationPortrait || orientation == UIInterfaceOrientationPortraitUpsideDown) ? YES: NO;
CGFloat complimentSize = [self getComplimentSize:videoTrack.naturalSize.height];
CGSize videoSize;
if(isPortrait) {
videoSize = CGSizeMake(videoTrack.naturalSize.height, complimentSize);
} else {
videoSize = CGSizeMake(complimentSize, videoTrack.naturalSize.height);
}
AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.renderSize = videoSize;
videoComposition.frameDuration = CMTimeMake(1, 30);
AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30) );
// rotate and position video
AVMutableVideoCompositionLayerInstruction* transformer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
CGFloat tx = (videoTrack.naturalSize.width-complimentSize)/2;
if (orientation == UIInterfaceOrientationPortrait || orientation == UIInterfaceOrientationLandscapeRight) {
// invert translation
tx *= -1;
}
// t1: rotate and position video since it may have been cropped to screen ratio
CGAffineTransform t1 = CGAffineTransformTranslate(videoTrack.preferredTransform, tx, 0);
// t2/t3: mirror video horizontally
CGAffineTransform t2 = CGAffineTransformTranslate(t1, isPortrait?0:videoTrack.naturalSize.width, isPortrait?videoTrack.naturalSize.height:0);
CGAffineTransform t3 = CGAffineTransformScale(t2, isPortrait?1:-1, isPortrait?-1:1);
[transformer setTransform:t3 atTime:kCMTimeZero];
instruction.layerInstructions = [NSArray arrayWithObject: transformer];
videoComposition.instructions = [NSArray arrayWithObject: instruction];
// export
exporter = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality] ;
exporter.videoComposition = videoComposition;
exporter.outputURL=[NSURL fileURLWithPath:outputPath];
exporter.outputFileType=AVFileTypeQuickTimeMovie;
[exporter exportAsynchronouslyWithCompletionHandler:^(void){
NSLog(@"Exporting done!");
// added export to library for testing
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:[NSURL fileURLWithPath:outputPath]]) {
[library writeVideoAtPathToSavedPhotosAlbum:[NSURL fileURLWithPath:outputPath]
completionBlock:^(NSURL *assetURL, NSError *error) {
NSLog(@"Saved to album");
if (error) {
}
}];
}
}];
我们在此处添加的是根据将视频尺寸裁剪为屏幕比例来获取视频新渲染尺寸的调用.缩小尺寸后，我们需要将位置转换为重新定位视频.所以我们抓住它的方向以将它移动到正确的方向.这将解决我们在 UIInterfaceOrientationLandscapeLeft 中看到的偏离中心的问题.最后CGAffineTransform t2,t3水平镜像视频.
What we added here is a call to get the new render size of the video based on cropping its dimensions to the screen ratio. Once we crop the size down, we need to translate the position to recenter the video. So we grab its orientation to move it in the proper direction. This will fix the off-center issue we saw with UIInterfaceOrientationLandscapeLeft. Finally CGAffineTransform t2, t3 mirror the video horizontally.
这是实现这一目标的两种新方法:
And here are the two new methods that make this happen:
- (CGFloat)getComplimentSize:(CGFloat)size {
CGRect screenRect = [[UIScreen mainScreen] bounds];
CGFloat ratio = screenRect.size.height / screenRect.size.width;
// we have to adjust the ratio for 16:9 screens
if (ratio == 1.775) ratio = 1.77777777777778;
return size * ratio;
}
- (UIInterfaceOrientation)orientationForTrack:(AVAsset *)asset {
UIInterfaceOrientation orientation = UIInterfaceOrientationPortrait;
NSArray *tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
if([tracks count] > 0) {
AVAssetTrack *videoTrack = [tracks objectAtIndex:0];
CGAffineTransform t = videoTrack.preferredTransform;
// Portrait
if(t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0) {
orientation = UIInterfaceOrientationPortrait;
}
// PortraitUpsideDown
if(t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0) {
orientation = UIInterfaceOrientationPortraitUpsideDown;
}
// LandscapeRight
if(t.a == 1.0 && t.b == 0 && t.c == 0 && t.d == 1.0) {
orientation = UIInterfaceOrientationLandscapeRight;
}
// LandscapeLeft
if(t.a == -1.0 && t.b == 0 && t.c == 0 && t.d == -1.0) {
orientation = UIInterfaceOrientationLandscapeLeft;
}
}
return orientation;
}
这些非常简单.唯一需要注意的是，在 getComplimentSize: 方法中，我们必须手动调整 16:9 的比例，因为 iPhone5+ 的分辨率在数学上低于真正的 16:9.
These are pretty straight forward. The only thing to note is that in the getComplimentSize: method we have to manually adjust the ratio for 16:9 since the iPhone5+ resolution is mathematically shy of true 16:9.
这篇关于使用 AVFoundation 裁剪 AVAsset 视频的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
