从VTCompressionOutputCallback中引用`self` [英] Referencing `self` from within a VTCompressionOutputCallback

问题描述

我目前正在尝试使用VideoToolbox对 AVCaptureVideoDataOutput 中的视频数据进行编码，但是在从 VTCompressionOutputCallback .

I'm currently trying to use VideoToolbox to encode video data from an AVCaptureVideoDataOutput, but I'm having an issue referencing self from within the VTCompressionOutputCallback.

我的代码如下:

...

var sessionRef: VTCompressionSession?

let outputCallback: VTCompressionOutputCallback = { _, _, status, _, sampleBuffer in
    guard status == noErr, let sampleBuffer = sampleBuffer else {
        return
    }

    debugPrint("[INFO]: outputCallback: sampleBuffer: \(sampleBuffer)")
}

let sessionErr = VTCompressionSessionCreate(allocator: nil,
                                            width: width,
                                            height: height,
                                            codecType: kCMVideoCodecType_H264,
                                            encoderSpecification: nil,
                                            imageBufferAttributes: nil,
                                            compressedDataAllocator: nil,
                                            outputCallback: outputCallback,
                                            refcon: nil,
                                            compressionSessionOut: UnsafeMutablePointer(&sessionRef))

...

这可以正常工作，并且可以按预期方式输出打印结果，但是一旦我尝试在 VTCompressionOutputCallback 中添加对 self 的引用，就会出现编译器错误，指出

That works fine, and the print outputs as expected, but as soon as I try and add a reference to self within the VTCompressionOutputCallback, it get a compiler error stating

不能从捕获上下文的闭包中形成C函数指针

如何在回调中使用 self ?

预先感谢您的帮助.

推荐答案

我想出了一个解决方案.

I figured out a solution.

VTCompressionSessionCreate 调用具有用于 outputCallbackRefCon 的参数，该参数将传递给 VTCompressionOutputCallback .

The VTCompressionSessionCreate call has a parameter for outputCallbackRefCon which gets passed along to the VTCompressionOutputCallback.

通过像这样将自己包装在 UnsafeMutableRawPointer 中

By wrapping self in an UnsafeMutableRawPointer like so

let unmanagedSelf = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())

我能够将该值传递到 refcon 参数下的 VTCompressionSessionCreate 中.然后，在回调内部，我可以使用

I was able to pass that value into the VTCompressionSessionCreate under the refcon parameter. Inside of the callback I was then able to do pull that value back out using

let scopedSelf = Unmanaged<ViewController>.fromOpaque(unmanagedSelf).takeUnretainedValue()

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