如何在AVMutableComposition中同时为多个视频层设置动画？

Question

我正在编写一段代码，从iOS设备上的多个图像和多个视频生成幻灯片放映视频。我可以用一个视频和多个图像来做到这一点，但我不知道如何将其增强为多个视频。

这里是the sample video，我能够用一个视频和两个图像生成。

这是准备出口商的主要程序。

// Prepare the temporary location to store generated video
NSURL * urlAsset = [NSURL fileURLWithPath:[StoryMaker tempFilePath:@"mov"]];

// Prepare composition and _exporter
AVMutableComposition *composition = [AVMutableComposition composition];
AVAssetExportSession* exporter = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetHighestQuality];
exporter.outputURL = urlAsset;
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = [self _addVideo:composition time:timeVideo];

这里是_addVideo：time：方法，该方法创建videoLayer。

-(AVVideoComposition*) _addVideo:(AVMutableComposition*)composition time:(CMTime)timeVideo {
    AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.renderSize = _sizeVideo;
    videoComposition.frameDuration = CMTimeMake(1,30); // 30fps
    AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,timeVideo) ofTrack:_baseVideoTrack atTime:kCMTimeZero error:nil];

    // Prepare the parent layer
    CALayer *parentLayer = [CALayer layer];
    parentLayer.backgroundColor = [UIColor blackColor].CGColor;
    parentLayer.frame = CGRectMake(0, 0, _sizeVideo.width, _sizeVideo.height);

    // Prepare images parent layer
    CALayer *imageParentLayer = [CALayer layer];
    imageParentLayer.frame = CGRectMake(0, 0, _sizeVideo.width, _sizeVideo.height);
    [parentLayer addSublayer:imageParentLayer];

    // Specify the perspecrtive view
    CATransform3D perspective = CATransform3DIdentity;
    perspective.m34 = -1.0 / imageParentLayer.frame.size.height;
    imageParentLayer.sublayerTransform = perspective;

    // Animations
    _beginTime = 1E-10;
    _endTime = CMTimeGetSeconds(timeVideo);

    CALayer* videoLayer = [self _addVideoLayer:imageParentLayer];
    [self _addAnimations:imageParentLayer time:timeVideo];

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

    // Prepare the instruction
    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    {
        instruction.timeRange = CMTimeRangeMake(kCMTimeZero, timeVideo);
        AVAssetTrack *videoTrack = [[composition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
        AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
        [layerInstruction setTransform:_baseVideoTrack.preferredTransform atTime:kCMTimeZero];
        instruction.layerInstructions = @[layerInstruction];
    }
    videoComposition.instructions = @[instruction];
    return videoComposition;
} 

_ addAnimation：time：方法添加图像图层，并计划包括_videoLayer在内的所有图层的动画。

到目前为止一切正常。

但是，我不知道如何将第二个视频添加到此幻灯片中。

《 AVFoundation编程指南》中的示例使用多个视频合成指令（AVMutableVideoCompositionInstruction）来组合两个视频，但只是将它们呈现为单个CALayer对象，该对象在videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer：inLayer：in方法（在AVVideoCompositionCoreAnimationTool的方法中）中指定。

我想将两个视频轨道渲染到两个单独的层（layer1和layer2）中，并分别对其进行动画处理，就像我正在处理与图像关联的层一样。

Answer 1

我也有这个问题，想制作多个视频的动画。我发现AVVideoCompositionCoreAnimationTool可以接受多个视频层，但是要注意的是它们是同一视频的多个实例。因此，我的解决方法是制作一个大视频，将2个视频彼此相邻放置，并使用遮罩在其自己的图层中显示每个视频。