使用AVFoundation裁剪AVAsset视频

时间：2014-01-12 16:36:33

标签： ios video avfoundation avassetexportsession

我正在使用AVCaptureMovieFileOutput录制一些视频。我使用AVLayerVideoGravityResizeAspectFill显示预览图层，稍微放大。我遇到的问题是最终视频较大，包含在预览期间不适合屏幕的额外图像。

这是预览及结果视频

enter image description here enter image description here

我是否可以使用CGRect指定要从视频剪切的AVAssetExportSession？

编辑----

当我将CGAffineTransformScale应用于AVAssetTrack时，它会缩放到视频中，并且AVMutableVideoComposition renderSize设置为view.bounds 。太棒了，还剩下一个问题。视频的宽度不会拉伸到正确的宽度，只会填充黑色。

编辑2 ---- 建议的问题/答案是不完整的..

我的一些代码：

在我的- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error方法中，我可以裁剪并调整视频大小。

- (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;
            }
        }
    }];
}

2 个答案:

答案 0 :(得分：20)

以下是我对您的问题的解释：您正在屏幕比例为4：3的设备上捕获视频，因此您的AVCaptureVideoPreviewLayer为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的视频“更大”。

如果您只想裁剪未预览的额外像素，请查看此http://www.netwalk.be/article/record-square-video-ios。本文介绍如何将视频裁剪为正方形。但是，您只需要进行一些修改即可裁剪为4：3。我已经去测试了这个，这是我做的改变：

获得视频的AVAssetTrack后，您需要计算新的高度。

// 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;

然后使用newHeight修改这两行。

videoComposition.renderSize = CGSizeMake(clipVideoTrack.naturalSize.height, newHeight);

CGAffineTransform t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height, -(clipVideoTrack.naturalSize.width - newHeight)/2 );

所以我们在这里做的是将renderSize设置为4：3的比例 - 确切的维度基于输入设备。然后，我们使用CGAffineTransform翻译视频位置，以便我们在AVCaptureVideoPreviewLayer中看到的内容是呈现给我们文件的内容。

修改：如果您想将它们放在一起并根据设备的屏幕比例裁剪视频（3：2,4：3,16：9）并考虑视频方向我们需要添加一些东西。

首先是修改后的示例代码，其中包含一些重要的更改：

// 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) {

             }
         }];
    }
}];

我们在这里添加的是调用以获取视频的新渲染大小，基于将其尺寸裁剪为屏幕比例。一旦我们缩小尺寸，我们需要转换位置以重新定位视频。所以我们抓住它的方向将它移向正确的方向。这将解决我们在UIInterfaceOrientationLandscapeLeft看到的偏心问题。最后CGAffineTransform t2, t3水平镜像视频。

以下是实现这一目标的两种新方法：

- (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，我们必须手动调整比例为16：9，因为iPhone5 +分辨率在数学上与真正的16：9无关。

答案 1 :(得分：2)

AVCaptureVideoDataOutput 是AVCaptureOutput的具体子类，用于处理正在捕获的视频中的未压缩帧或访问压缩帧。

AVCaptureVideoDataOutput的实例会生成您可以使用其他媒体API处理的视频帧。您可以使用captureOutput:didOutputSampleBuffer:fromConnection:委托方法访问框架。

配置会话 您可以在会话中使用预设来指定所需的图像质量和分辨率。预设是一个常数，用于标识多种可能配置中的一种;在某些情况下，实际配置是特定于设备的：

https://developer.apple.com/library/mac/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/04_MediaCapture.html

这些预设为各种设备所代表的实际值，请参阅“Saving to a Movie File”和“捕捉静止图像”。

如果要设置特定于大小的配置，则应在设置之前检查它是否受支持：

if ([session canSetSessionPreset:AVCaptureSessionPreset1280x720]) {
    session.sessionPreset = AVCaptureSessionPreset1280x720;
}
else {
    // Handle the failure.
}
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