ios - 尝试使用 AVFoundation 在同一帧中组合三个不同的视频轨道时多次获取第一个视频轨道

Question

我想将多个视频及其音频合并到一个视频帧中，因为我正在使用 AVFoundation 框架。

为此，我创建了一个接受 Assets 数组的方法，截至目前，我正在传递三个不同视频的 Assets 。

到目前为止，我已经合并了他们的音频，但问题在于视频帧，其中只有第一个 Assets 的视频在每一帧中重复。

我正在使用下面的代码来组合视频，这些视频完美地组合了所有三个视频的音频，但输入数组中的第一个视频重复了三次，这是主要问题:

我想要帧中的所有三个不同视频。

func merge(Videos aArrAssets: [AVAsset]){

        let mixComposition = AVMutableComposition()

        func setup(asset aAsset: AVAsset, WithComposition aComposition: AVMutableComposition) -> AVAssetTrack{

            let aMutableCompositionVideoTrack = aComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
            let aMutableCompositionAudioTrack = aComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)

            let aVideoAssetTrack: AVAssetTrack = aAsset.tracks(withMediaType: .video)[0]
            let aAudioAssetTrack: AVAssetTrack = aAsset.tracks(withMediaType: .audio)[0]

            do{
            try aMutableCompositionVideoTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: aAsset.duration), of: aVideoAssetTrack, at: .zero)
            try aMutableCompositionAudioTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: aAsset.duration), of: aAudioAssetTrack, at: .zero)
            }catch{}

            return aVideoAssetTrack
        }

        let aArrVideoTracks = aArrAssets.map { setup(asset: $0, WithComposition: mixComposition) }

        var aArrLayerInstructions : [AVMutableVideoCompositionLayerInstruction] = []

        //Transform every video
        var aNewHeight : CGFloat = 0
        for (aIndex,aTrack) in aArrVideoTracks.enumerated(){

            aNewHeight += aIndex > 0 ? aArrVideoTracks[aIndex - 1].naturalSize.height : 0

            let aLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: aTrack)
            let aFristTransform = CGAffineTransform(translationX: 0, y: aNewHeight)

            aLayerInstruction.setTransform(aFristTransform, at: .zero)
            aArrLayerInstructions.append(aLayerInstruction)
        }


        let aTotalTime = aArrVideoTracks.map { $0.timeRange.duration }.max()

        let aInstruction = AVMutableVideoCompositionInstruction()
        aInstruction.timeRange = CMTimeRangeMake(start: .zero, duration: aTotalTime!)
        aInstruction.layerInstructions = aArrLayerInstructions

        let aVideoComposition = AVMutableVideoComposition()
        aVideoComposition.instructions = [aInstruction]
        aVideoComposition.frameDuration = CMTimeMake(value: 1, timescale: 30)

        let aTotalWidth = aArrVideoTracks.map { $0.naturalSize.width }.max()!
        let aTotalHeight = aArrVideoTracks.map { $0.naturalSize.height }.reduce(0){ $0 + $1 }
        aVideoComposition.renderSize = CGSize(width: aTotalWidth, height: aTotalHeight)


        saveVideo(WithAsset: mixComposition, videoComp : aVideoComposition) { (aError, aUrl) in
            print("Location : \(String(describing: aUrl))")
        }
    }

    private func saveVideo(WithAsset aAsset : AVAsset, videoComp : AVVideoComposition, completion: @escaping (_ error: Error?, _ url: URL?) -> Void){


        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "ddMMyyyy_HHmm"
        let date = dateFormatter.string(from: NSDate() as Date)

        // Exporting
        let savePathUrl: URL = URL(fileURLWithPath: NSHomeDirectory() + "/Documents/newVideo_\(date).mov")
        do { // delete old video
            try FileManager.default.removeItem(at: savePathUrl)
        } catch { print(error.localizedDescription) }


        let assetExport: AVAssetExportSession = AVAssetExportSession(asset: aAsset, presetName: AVAssetExportPresetMediumQuality)!
        assetExport.outputFileType = .mov
        assetExport.outputURL = savePathUrl
//        assetExport.shouldOptimizeForNetworkUse = true
        assetExport.videoComposition = videoComp

        assetExport.exportAsynchronously { () -> Void in
            switch assetExport.status {
            case .completed:
                print("success")
                completion(nil, savePathUrl)
            case .failed:
                print("failed \(assetExport.error?.localizedDescription ?? "error nil")")
                completion(assetExport.error, nil)
            case .cancelled:
                print("cancelled \(assetExport.error?.localizedDescription ?? "error nil")")
                completion(assetExport.error, nil)
            default:
                print("complete")
                completion(assetExport.error, nil)
            }
        }
    }

我知道我在代码中做错了一些事情，但无法弄清楚在哪里，所以我需要一些帮助来找出它。

提前致谢。

Answer 1

您的问题是，当您构建AVMutableVideoCompositionLayerInstruction 时，aTrack 引用是对您设置的原始 Assets 轨道的引用

let aVideoAssetTrack: AVAssetTrack = aAsset.tracks(withMediaType: .video)[0]

它的 trackID 是 1，因为它是源 AVAsset 中的第一首轨道。因此，当您检查您的 aArrLayerInstructions 时，您会看到您的指令的 trackID 都是 1。这就是为什么您会收到 3 次第一个视频

(lldb) p aArrLayerInstructions[0].trackID
(CMPersistentTrackID) $R8 = 1
(lldb) p aArrLayerInstructions[1].trackID
(CMPersistentTrackID) $R10 = 1
...

解决方案是在构建合成层指令时不枚举源轨道，而是枚举合成轨道。

let tracks = mixComposition.tracks(withMediaType: .video)
for (aIndex,aTrack) in tracks.enumerated(){
...

如果你这样做，你会为你的图层指令获得正确的 trackIDs

(lldb) p aArrLayerInstructions[0].trackID
(CMPersistentTrackID) $R2 = 1
(lldb) p aArrLayerInstructions[1].trackID
(CMPersistentTrackID) $R4 = 3
...