iOS 中的裁剪视频在视频周围看到奇怪的绿线

Posted 2023-02-25

【中文标题】iOS 中的裁剪视频在视频周围看到奇怪的绿线

【英文标题】：Crop video in iOS see weird green line around video

【发布时间】：2015-04-08 03:53:34

【问题描述】：

大家好，我正在裁剪从 iPhone 上的相机拍摄的视频，然后将其裁剪并像这样播放。但是，当我这样做时，我会在视频的底部和右侧看到一条奇怪的绿线？不知道为什么会发生这种情况或如何解决它。这是我的裁剪方式。

- (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;



- (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


//    NSLog(@"CALLED");
    //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;
//    NSLog(@"width: %f - height: %f - x: %f - y: %f", cropWidth, cropHeight, cropOffX, cropOffY);

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;

然后我像这样玩和调用作物。

AVAsset *assest = [AVAsset assetWithURL:self.videoURL];


NSString * documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *exportPath = [documentsPath stringByAppendingFormat:@"/croppedvideo.mp4"];
NSURL *exportUrl = [NSURL fileURLWithPath:exportPath];


AVAssetExportSession *exporter = [AVAssetExportSession exportSessionWithAsset:assest presetName:AVAssetExportPresetLowQuality];


[self applyCropToVideoWithAsset:assest AtRect:CGRectMake(self.view.frame.size.width/2 - 57.5 - 5, self.view.frame.size.height / 2 - 140, 115, 85) OnTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(assest.duration.value, 1))
                    ExportToUrl:exportUrl ExistingExportSession:exporter WithCompletion:^(BOOL success, NSError *error, NSURL *videoUrl) 
AVPlayer *player = [AVPlayer playerWithURL:videoUrl];

AVPlayerLayer *layer = [AVPlayerLayer playerLayerWithPlayer:player];
layer.frame = CGRectMake(125, 365, 115, 115);
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 400, 400)];
[view.layer addSublayer:layer];
[self.view addSubview:view];
[player play];

如果你想测试这个，只需复制粘贴代码，然后设置一个视频，你就会看到我在说什么。

感谢您花时间帮助我，我知道这是一段相当多的代码。

【参考方案1】：

ios 编码器或视频格式本身都有宽度要求。尝试使宽度均匀或可被 4 整除。

我不知道对高度有类似的要求，但这也值得一试。

我从来没有发现它记录在案，但是要求均匀度有一定的意义，因为 h.264 使用 4:2:0 yuv 颜色空间，其中 UV 分量的大小（在两个维度上）是Y 通道，具有视频的整体尺寸。如果这些尺寸不均匀，那么 UV 尺寸就不是完整的。

附言在这些情况下，暗示是神秘的绿色。我认为它对应于 YUV 中的 0,0,0。

【讨论】：

它必须为宽度和高度都完成，但是哇，这太奇怪了

酷。是 2 还是 4 的倍数？

【参考方案2】：

@Rhythmic 的回答拯救了我的一天。

在我的应用中，我需要根据屏幕宽度大小的方形视频。因此，对于 iPhone 5，这是 320 像素，对于 iPhone 6，这是 375 像素。

所以我遇到了 iPhone 6 尺寸分辨率的相同绿线问题。因为它的屏幕尺寸宽度是 375 像素。并且不能被 2 或 4 整除。

为此，我们进行了以下更改：

 AVMutableVideoComposition *MainCompositionInst = [AVMutableVideoComposition videoComposition];
    MainCompositionInst.instructions = [NSArray arrayWithObject:MainInstruction];
    MainInstruction.timeRange = range;
    
    MainCompositionInst.frameDuration = VideoFrameDuration; //Constants
    MainCompositionInst.renderScale = VideoRenderScale; //Constants
        
    if ((int)SCREEN_WIDTH % 2 == 0)
        MainCompositionInst.renderSize = CGSizeMake(SCREEN_WIDTH, SCREEN_WIDTH);
    else // This does the trick
        MainCompositionInst.renderSize = CGSizeMake(SCREEN_WIDTH+1, SCREEN_WIDTH+1); 

只需再添加一个像素，它就可以被 2 或 4 整除。

【讨论】：

聪明的解释，我看过@Rhythmic 的回答，它实际上是一个很好的回答。但当事不宜迟。你赢了。 ;) 所以为你 +1。