如何让AVAssetReader循环？

Question

嗨，我一直在试图弄清楚如何在GPUImage2中实现电影循环，但到目前为止还没有成功。GPUImage2中的MovieInput类使用AVAssetReader播放电影文件，因此我研究了循环AVAssetReader的方法。我在StackOverFlow上找到了这个关于这个话题的问题。AVFoundation to reproduce a video loop

最好的答案是"AVAssetReader不支持查找或重新启动，它本质上是一个顺序解码器。你必须创建一个新的AVAssetReader对象来再次读取相同的样本。“

我试图弄清楚如何将旧的assetReader连接到新的，但我并不是很成功，它每次都崩溃了。

有人建议我尝试这样做，但我不太确定如何编写函数generateAssetReader。

public func start() {
    self.assetReader = generateAssetReader(asset: asset, readAudio: readAudio, videoOutputSettings: videoOutputSettings, audioOutputSettings: audioOutputSettings)

 asset.loadValuesAsynchronously(forKeys:["tracks"], completionHandler:{
            DispatchQueue.global(priority:DispatchQueue.GlobalQueuePriority.default).async(execute: {
                guard (self.asset.statusOfValue(forKey: "tracks", error:nil) == .loaded) else { return }

                guard self.assetReader.startReading() else {
                    print("Couldn't start reading")
                    return
                }

                var readerVideoTrackOutput:AVAssetReaderOutput? = nil;

                for output in self.assetReader.outputs {
                    if(output.mediaType == AVMediaTypeVideo) {
                        readerVideoTrackOutput = output;
                    }
                }

                while (self.assetReader.status == .reading) {
                    self.readNextVideoFrame(from:readerVideoTrackOutput!)
                }


    if assetReader.status == .completed {
        assetReader.cancelReading()
        self.assetReader = nil
        if self.loop {
            self.start()
        } else {
            self.endProcessing()
        }
    }
}

有没有人有办法解决这个循环问题？这是指向MovieInput类的完整代码的链接。https://github.com/BradLarson/GPUImage2/blob/master/framework/Source/iOS/MovieInput.swift

Answer 1

我找到了答案，以防有人想知道。

    public func createReader() -> AVAssetReader
{
    var assetRead:AVAssetReader!
    do{
        assetRead = try AVAssetReader.init(asset: self.asset)

        let outputSettings:[String:AnyObject] = [(kCVPixelBufferPixelFormatTypeKey as String):NSNumber(value:Int32(kCVPixelFormatType_420YpCbCr8BiPlanarFullRange))]
        let readerVideoTrackOutput = AVAssetReaderTrackOutput(track:self.asset.tracks(withMediaType: AVMediaTypeVideo)[0], outputSettings:outputSettings)
        readerVideoTrackOutput.alwaysCopiesSampleData = false

        assetRead.add(readerVideoTrackOutput)
    }catch{

    }

    return assetRead
}

public func start() {
    self.assetReader = createReader()
    asset.loadValuesAsynchronously(forKeys:["tracks"], completionHandler:{
        DispatchQueue.global(priority:DispatchQueue.GlobalQueuePriority.default).async(execute: {
            guard (self.asset.statusOfValue(forKey: "tracks", error:nil) == .loaded) else { return }

            guard self.assetReader.startReading() else {
                print("Couldn't start reading")
                return
            }

            var readerVideoTrackOutput:AVAssetReaderOutput? = nil;

            for output in self.assetReader.outputs {
                if(output.mediaType == AVMediaTypeVideo) {
                    readerVideoTrackOutput = output;
                }
            }

            while (self.assetReader.status == .reading) {
                self.readNextVideoFrame(from:readerVideoTrackOutput!)
            }

            if (self.assetReader.status == .completed) {
                self.assetReader.cancelReading()

                if (self.loop) {
                    // TODO: Restart movie processing
                    self.start()
                } else {
                    self.endProcessing()
                }
            }
        })
    })
}