两层显示相同的视频

Question

我正在为视频创建两个图层，并尝试在每个单独的图层上显示我自己的 URL 和视频。我做错了什么？我在视频层和覆盖层上仅显示最终结果中的第一个视频。 问题：在最终输出视频中，我在视频层和覆盖层上仅看到来自第一个 URL (videoURL) 的视频。覆盖层未按预期显示来自overlayVideoURL 的视频。
我尝试过的： 我检查了 CALayer 框架并确认它们设置正确。 已验证 AVVideoCompositionCoreAnimationTool 是否正确使用。 确认 AVMutableComposition 已插入两条轨道。 问题： 我设置视频图层的方式是否有错误？ 如何保证每一层正确显示各自的视频？ 其他详细信息： 视频已正确加载并插入到 AVMutableComposition 中。 最终的合成仅在两层上显示来自 videoURL 的视频。

 func makeVideo(videoURL: URL, overlayVideoURL: URL, forName name: String, onComplete: @escaping (URL?) -> Void) {
            let asset = AVURLAsset(url: videoURL)
            let overlayAsset = AVURLAsset(url: overlayVideoURL)
            let composition = AVMutableComposition()
            guard
                let compositionTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid),
                let assetTrack = asset.tracks(withMediaType: .video).first,
                let overlayCompositionTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid),
                let overlayAssetTrack = overlayAsset.tracks(withMediaType: .video).first
            else {
                print("Something is wrong with the assets.")
                onComplete(nil)
                return
            }
            do {
                let timeRange = CMTimeRange(start: .zero, duration: asset.duration)
                try compositionTrack.insertTimeRange(timeRange, of: assetTrack, at: .zero)
                try overlayCompositionTrack.insertTimeRange(timeRange, of: overlayAssetTrack, at: .zero)
            } catch {
                print(error)
                onComplete(nil)
                return
            } 
            let videoInfo = orientation(from: assetTrack.preferredTransform)
            let videoSize = videoInfo.isPortrait ? CGSize(width: assetTrack.naturalSize.height, height: assetTrack.naturalSize.width) : assetTrack.naturalSize
            let videoComposition = AVMutableVideoComposition()
            videoComposition.renderSize = videoSize
            videoComposition.frameDuration = CMTime(value: 1, timescale: 30) 
            let instruction = AVMutableVideoCompositionInstruction()
            instruction.timeRange = CMTimeRange(start: .zero, duration: composition.duration)
            let layerInstruction = compositionLayerInstruction(for: compositionTrack, assetTrack: assetTrack)
            let overlayLayerInstruction = compositionLayerInstruction(for: overlayCompositionTrack, assetTrack: overlayAssetTrack)
            instruction.layerInstructions = [layerInstruction, overlayLayerInstruction]
            videoComposition.instructions = [instruction]
            let videoLayer = CALayer()
            videoLayer.frame = CGRect(origin: .zero, size: videoSize)
            let overlayVideoLayer = CALayer()
            overlayVideoLayer.frame = CGRect(x: videoSize.width / 4, y: videoSize.height / 4, width: videoSize.width / 2, height: videoSize.height / 2)
            let outputLayer = CALayer()
            outputLayer.frame = CGRect(origin: .zero, size: videoSize)
            outputLayer.addSublayer(videoLayer)
            outputLayer.addSublayer(overlayVideoLayer)
            videoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayers: [videoLayer, overlayVideoLayer], in: outputLayer)
            guard let export = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality) else {
                print("Cannot create export session.")
                onComplete(nil)
                return
            }
            let videoName = UUID().uuidString
            let exportURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(videoName).appendingPathExtension("mov")
            export.videoComposition = videoComposition
            export.outputFileType = .mov
            export.outputURL = exportURL
            export.exportAsynchronously {
                DispatchQueue.main.async {
                    switch export.status {
                    case .completed:
                        onComplete(exportURL)
                    default:
                        print("Something went wrong during export.")
                        print(export.error ?? "unknown error")
                        onComplete(nil)
                    }
                }
            }
        }

Answer 1

尝试使用

AVMutableVideoCompositionLayerInstruction

而不是

AVMutableVideoComposition

。计划是这样的：

// Here how to build it:
let mainInstruction = AVMutableVideoCompositionInstruction()
// Set time of your result video duration
mainInstruction.timeRange = timeRange
// For each video you'll need a separate AVMutableVideoCompositionInstruction
let videoInstruction = AVMutableVideoCompositionInstruction()
let overlayInstruction = AVMutableVideoCompositionInstruction()
// Now how to build and setup those instructions
// Here's your asset
let asset = AVAsset(url: url)
if let audioTrack = asset.tracks(withMediaType: .audio).first,
   let compositionAudioTrack = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid) {
    // Add audio track
}
let track = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)!
try! track.insertTimeRange(CMTimeRange(start: .zero, duration: asset.duration), of: asset.tracks(withMediaType: .video).first!, at: .zero)
let instruction /*videoInstruction/overlayInstruction*/ = AVMutableVideoCompositionLayerInstruction(assetTrack: track)
/* frameTransform shoule be calculated to move video track to the proper location on the layer */
instruction.setTransform(transform.concatenating(frameTransform), at: .zero)
// It will combine instructions for several layers
mainInstruction.layerInstructions = [videoInstruction, overlayInstruction]
// Video composition should have only one instruction
videoComposition.instructions = [mainInstruction]
// Then apply add videoComposition to a single layer, this single layer will render both videos in the locations determined by trannsform
videoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: parentLayer)

抱歉代码混乱，它所基于的示例更加混乱，所以我尝试从中提取重要的内容