我正在尝试在iOS 4.3上使用AVMutableComposition,AVMutableVideoComposition和AVVideoCompositionCoreAnimationTool,将CALayer制作成纵向模式视频(导出).这一切都在景观中起作用.然而,如果我以纵向拍摄视频,则AVVideoCompositionCoreAnimationTool忽略了视频轨道上的变换.也就是说,对于纵向模式视频,我将AVMutableCompositionTrack.preferredTransform设置为原始资源视频轨道的preferredTransform值.只要我不使用AVVideoCompositionCoreAnimationTool,这是有效的,视频以纵向模式出现.然而,一旦添加了AVVideoCompositionCoreAnimationTool和CALayer,文件就会出现. (CALayer正确显示,但其后面的视频在其侧面,文件的宽高比关闭).我已经尝试将变换应用于CALayer,并在ACVideoComposition中设置变换.这两个都不会改变文件的方向(它仍然是480×369,而不是360×480).有没有办法使用AVVideoCompositionCoreAnimationTool渲染纵向模式视频？

首先我设置一个AVMutableComposition和AVMutableVideoComposition

AVMutableComposition *composition = [AVMutableComposition composition];
AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVURLAsset *videoAsset = [AVURLAsset URLAssetWithURL:url options:nil];
CMTimeRange timeRange = CMTimeRangeMake(kCMTimeZero,[videoAsset duration]);
AVAssetTrack *clipVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

CGSize videoSize = CGSizeApplyAffineTransform(clipVideoTrack.naturalSize,clipVideoTrack.preferredTransform);
videoSize.width = fabs(videoSize.width);
videoSize.height = fabs(videoSize.height);

CMTime titleDuration = CMTimeMakeWithSeconds(5,600);
CMTimeRange titleRange = CMTimeRangeMake(kCMTimeZero,titleDuration);

[compositionVideoTrack insertTimeRange:titleRange ofTrack:nil atTime:kCMTimeZero error:nil];
[compositionVideoTrack insertTimeRange:timeRange ofTrack:clipVideoTrack atTime:titleDuration error:nil];
compositionVideoTrack.preferredTransform = clipVideoTrack.preferredTransform;

AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
AVMutableVideoCompositionInstruction *passThroughInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
passThroughInstruction.timeRange = CMTimeRangeMake(kCMTimeZero,[composition duration]);
AVAssetTrack *videoTrack = [[composition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
AVMutableVideoCompositionLayerInstruction *passThroughLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];    
passThroughInstruction.layerInstructions = [NSArray arrayWithObject:passThroughLayer];
videoComposition.instructions = [NSArray arrayWithObject:passThroughInstruction];       
videoComposition.frameDuration = CMTimeMake(1,30); 
videoComposition.renderSize = videoSize;
videoComposition.renderScale = 1.0;

和一个标题的CALayer

CALayer *animationLayer = [CALayer layer];
animationLayer.bounds = CGRectMake(0,videoSize.width,videoSize.height);

CATextLayer *titleLayer = [CATextLayer layer];
titleLayer.string = [effect valueForKey:@"title"];
titleLayer.font = [effect valueForKey:@"font"];
titleLayer.fontSize = 30;

titleLayer.alignmentMode = kCAAlignmentCenter;
titleLayer.bounds = CGRectMake(0,videoSize.height / 6);

[animationLayer addSublayer:titleLayer];
titleLayer.anchorPoint =  CGPointMake(0.5,0.5);
titleLayer.position = CGPointMake(CGRectGetMidX(layer.bounds),CGRectGetMidY(layer.bounds));    

CABasicAnimation *fadeAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
fadeAnimation.fromValue = [NSNumber numberWithFloat:1.0];
fadeAnimation.toValue = [NSNumber numberWithFloat:0.0];
fadeAnimation.additive = NO;
fadeAnimation.removedOnCompletion = NO;
fadeAnimation.beginTime = 3.5;
fadeAnimation.duration = 1.0;
fadeAnimation.fillMode = kCAFillModeBoth;
[titleLayer addAnimation:fadeAnimation forKey:nil];

最后,我将CALayer添加到AVMutableVideoComposition

CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];

parentLayer.bounds = CGRectMake(0,videoSize.height);
parentLayer.anchorPoint =  CGPointMake(0,0);
parentLayer.position = CGPointMake(0,0);

videoLayer.bounds = CGRectMake(0,videoSize.height);
[parentLayer addSublayer:videoLayer];
videoLayer.anchorPoint =  CGPointMake(0.5,0.5);
videoLayer.position = CGPointMake(CGRectGetMidX(parentLayer.bounds),CGRectGetMidY(parentLayer.bounds));
[parentLayer addSublayer:layer];    
animationLayer.anchorPoint =  CGPointMake(0.5,0.5);
animationLayer.position = CGPointMake(CGRectGetMidX(parentLayer.bounds),CGRectGetMidY(parentLayer.bounds));
videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

并出口！

AVAssetExportSession *exportSession = [[[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetMediumQuality] autorelease];
exportSession.videoComposition = videoComposition; 

NSURL *segmentFileURL = //some local URL
exportSession.outputFileType = @"com.apple.quicktime-movie";
exportSession.outputURL = segmentFileURL;


[exportSession exportAsynchronouslyWithCompletionHandler:^{
    switch ([exportSession status]) {
        case AVAssetExportSessionStatusFailed:
            Log(@"Export Failed: %@",[exportSession error]);
            break;
        case AVAssetExportSessionStatusCancelled:
            Log(@"Export canceled");
            break;
        case AVAssetExportSessionStatusCompleted:
            Log(@"Export done");
            break;
    }
}];

此代码在横向模式下工作,并且如果我删除行,也以纵向方式.Composition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer：videoLayer inLayer：parentLayer];