CALayer.contents无法在AVMutableComposition中正确呈现

Question

我有一个非常简单的方法,可以生成一个视频,其中包含覆盖整个视频合成的静态背景图像,以及位于视频底部的较小的,部分透明的图像(水印样式).

背景图像正确渲染,看起来与图像查看器中的外观完全相同.但是,应该在视频底部呈现的图像是倾斜/失真的.

源代码可以在这里下载,在GitHub上.

我的代码的预期输出(所需视频输出的模型):

我的代码的实际输出(来自iOS模拟器的部分屏幕截图):

如您所见,页脚图像以45度角和略微波浪形倾斜.

以下是我目前用于生成视频的代码.我已经尝试了每个可能的内容组合的重力为页脚图像,没有运气.所有其他的例子,我只是看到设置一个CGImageRef为图层的contents然后设置bounds,position并anchorPoint以相应的值.我没有看到任何其他设置任何其他属性的示例.我已经阅读了几乎所有AVFoundation的文档,看看是否有我失踪的设置,但我还没有看到任何明显的东西.

任何建议将不胜感激.谢谢!

接口声明:

CGSize _renderingSize;
float _displayDuration;

AVMutableComposition *mutableComposition;
AVMutableVideoComposition *videoComposition;
AVMutableCompositionTrack *mutableCompositionVideoTrack;
AVAssetExportSession *exporter;

ViewDidLoad设置:

_renderingSize = CGSizeMake(640, 360);
_displayDuration = 2.0;

渲染代码块:

    mutableComposition = [AVMutableComposition composition];
    mutableCompositionVideoTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.renderSize = _renderingSize;
    videoComposition.frameDuration = CMTimeMake(1, 30);

    CALayer *parentLayer = [CALayer layer];
    CALayer *videoLayer = [CALayer layer];
    parentLayer.frame = CGRectMake(0, 0, videoComposition.renderSize.width, videoComposition.renderSize.height);
    videoLayer.frame = CGRectMake(0, 0, videoComposition.renderSize.width, videoComposition.renderSize.height);
    [parentLayer addSublayer:videoLayer];

    videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

    NSString *path = [[NSBundle mainBundle] pathForResource:@"blank_1080p" ofType:@"mp4"];
    NSURL *url = [NSURL fileURLWithPath:path];
    AVAsset *asset = [AVAsset assetWithURL:url];
    AVAssetTrack *track = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    [mutableCompositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,CMTimeMakeWithSeconds(_displayDuration, 600)) ofTrack:track atTime:kCMTimeZero error:nil];

    CALayer *imageLayer = [CALayer layer];
    imageLayer.bounds = parentLayer.frame;
    imageLayer.anchorPoint = CGPointMake(0.5, 0.5);
    imageLayer.position = CGPointMake(CGRectGetMidX(imageLayer.bounds), CGRectGetMidY(imageLayer.bounds));
    imageLayer.contents = (id)[UIImage imageNamed:@"background.png"].CGImage;
    imageLayer.contentsGravity = kCAGravityResizeAspectFill;
    [parentLayer addSublayer:imageLayer];

    UIImage *testImage = [UIImage imageNamed:@"bannerTextLayer.png"];

    CALayer *footerLayer = [CALayer layer];
    footerLayer.bounds = CGRectMake(0, 0, 540, 40);
    footerLayer.anchorPoint = CGPointMake(0.5, 0.5);
    footerLayer.position = CGPointMake(CGRectGetMidX(footerLayer.bounds), CGRectGetMidY(footerLayer.bounds));
    footerLayer.contents = (id)testImage.CGImage;
    footerLayer.contentsGravity = kCAGravityResizeAspectFill;
    [parentLayer addSublayer:footerLayer];

    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(_displayDuration, 600));
    videoComposition.instructions = @[instruction];

    exporter = [[AVAssetExportSession alloc] initWithAsset:mutableComposition presetName:AVAssetExportPresetHighestQuality];
    exporter.outputURL = videoURL ;
    exporter.videoComposition = videoComposition;
    exporter.outputFileType= AVFileTypeMPEG4;
    exporter.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(_displayDuration, 600));
    exporter.shouldOptimizeForNetworkUse = YES;

    [exporter exportAsynchronouslyWithCompletionHandler:^(void){
        switch (exporter.status) {
            case AVAssetExportSessionStatusFailed:{
                NSLog(@"Fail: %@", exporter.error);
                break;
            }
            case AVAssetExportSessionStatusCompleted:{
                NSLog(@"Success");

                dispatch_async(dispatch_get_main_queue(), ^{
                    if (self.moviePlayer)
                        [self.moviePlayer.view removeFromSuperview];

                    self.moviePlayer = [[MPMoviePlayerController alloc] initWithContentURL:videoURL];

                    self.moviePlayer.view.frame = CGRectMake(0, 0, 320, 180);
                    [self.moviePlayer setControlStyle:MPMovieControlStyleNone];

                    [self.previewView addSubview:self.moviePlayer.view];
                    [self.moviePlayer play];

                });

                break;
            }
            default:
                break;
        }
    }];

Answer 1

iOS模拟器7.0及更高版本存在使用AVExportSession呈现视频的错误.如果你将在实际设备上测试它,输出将是你想要的,它不会倾斜.