5

我很难想出在任何 iOS 设备上可靠地复制 CVPixelBuffer 的代码。在我在 iPad Pro 上尝试之前，我的第一次尝试效果很好：

extension CVPixelBuffer {
    func deepcopy() -> CVPixelBuffer? {
        let width = CVPixelBufferGetWidth(self)
        let height = CVPixelBufferGetHeight(self)
        let format = CVPixelBufferGetPixelFormatType(self)
        var pixelBufferCopyOptional:CVPixelBuffer?
        CVPixelBufferCreate(nil, width, height, format, nil, &pixelBufferCopyOptional)
        if let pixelBufferCopy = pixelBufferCopyOptional {
            CVPixelBufferLockBaseAddress(self, kCVPixelBufferLock_ReadOnly)
            CVPixelBufferLockBaseAddress(pixelBufferCopy, 0)
            let baseAddress = CVPixelBufferGetBaseAddress(self)
            let dataSize = CVPixelBufferGetDataSize(self)
            let target = CVPixelBufferGetBaseAddress(pixelBufferCopy)
            memcpy(target, baseAddress, dataSize)
            CVPixelBufferUnlockBaseAddress(pixelBufferCopy, 0)
            CVPixelBufferUnlockBaseAddress(self, kCVPixelBufferLock_ReadOnly)
        }
        return pixelBufferCopyOptional
    }
}

以上在 iPad Pro 上崩溃，因为CVPixelBufferGetDataSize(self)略大于CVPixelBufferGetDataSize(pixelBufferCopy)，所以 memcpy 写入未分配的内存。

所以我放弃了这个并尝试了这个：

func copy() -> CVPixelBuffer?
{
    precondition(CFGetTypeID(self) == CVPixelBufferGetTypeID(), "copy() cannot be called on a non-CVPixelBuffer")

    var _copy: CVPixelBuffer?

    CVPixelBufferCreate(
        nil,
        CVPixelBufferGetWidth(self),
        CVPixelBufferGetHeight(self),
        CVPixelBufferGetPixelFormatType(self),
        CVBufferGetAttachments(self, .shouldPropagate),
        &_copy)

    guard let copy = _copy else { return nil }

    CVPixelBufferLockBaseAddress(self, .readOnly)
    CVPixelBufferLockBaseAddress(copy, [])
    defer
    {
        CVPixelBufferUnlockBaseAddress(copy, [])
        CVPixelBufferUnlockBaseAddress(self, .readOnly)
    }

    for plane in 0 ..< CVPixelBufferGetPlaneCount(self)
    {
        let dest        = CVPixelBufferGetBaseAddressOfPlane(copy, plane)
        let source      = CVPixelBufferGetBaseAddressOfPlane(self, plane)
        let height      = CVPixelBufferGetHeightOfPlane(self, plane)
        let bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(self, plane)

        memcpy(dest, source, height * bytesPerRow)
    }

    return copy
}

这适用于我的两个测试设备，但它刚刚接触到实际客户，结果证明它在 iPad 6 上崩溃（到目前为止只有那个设备）。这是一个再次EXC_BAD_ACCESS呼吁memcpy()。

考虑到让它可靠地工作似乎有多困难，没有一个简单的 API 调用似乎很疯狂。还是我让它变得比需要的更难？感谢您的任何建议！

4

2 回答 2

8

这个问答组合是纯金的。让我通过轻微的重构和一些控制流来增加价值，以解决CVPixelBuffers没有平面的问题。

public extension CVPixelBuffer {
    func copy() throws -> CVPixelBuffer {
        precondition(CFGetTypeID(self) == CVPixelBufferGetTypeID(), "copy() cannot be called on a non-CVPixelBuffer")

        var _copy: CVPixelBuffer?

        let width = CVPixelBufferGetWidth(self)
        let height = CVPixelBufferGetHeight(self)
        let formatType = CVPixelBufferGetPixelFormatType(self)
        let attachments = CVBufferGetAttachments(self, .shouldPropagate)

        CVPixelBufferCreate(nil, width, height, formatType, attachments, &_copy)

        guard let copy = _copy else {
            throw PixelBufferCopyError.allocationFailed
        }

        CVPixelBufferLockBaseAddress(self, .readOnly)
        CVPixelBufferLockBaseAddress(copy, [])

        defer {
            CVPixelBufferUnlockBaseAddress(copy, [])
            CVPixelBufferUnlockBaseAddress(self, .readOnly)
        }

        let pixelBufferPlaneCount: Int = CVPixelBufferGetPlaneCount(self)


        if pixelBufferPlaneCount == 0 {
            let dest = CVPixelBufferGetBaseAddress(copy)
            let source = CVPixelBufferGetBaseAddress(self)
            let height = CVPixelBufferGetHeight(self)
            let bytesPerRowSrc = CVPixelBufferGetBytesPerRow(self)
            let bytesPerRowDest = CVPixelBufferGetBytesPerRow(copy)
            if bytesPerRowSrc == bytesPerRowDest {
                memcpy(dest, source, height * bytesPerRowSrc)
            }else {
                var startOfRowSrc = source
                var startOfRowDest = dest
                for _ in 0..<height {
                    memcpy(startOfRowDest, startOfRowSrc, min(bytesPerRowSrc, bytesPerRowDest))
                    startOfRowSrc = startOfRowSrc?.advanced(by: bytesPerRowSrc)
                    startOfRowDest = startOfRowDest?.advanced(by: bytesPerRowDest)
                }
            }

        }else {
            for plane in 0 ..< pixelBufferPlaneCount {
                let dest        = CVPixelBufferGetBaseAddressOfPlane(copy, plane)
                let source      = CVPixelBufferGetBaseAddressOfPlane(self, plane)
                let height      = CVPixelBufferGetHeightOfPlane(self, plane)
                let bytesPerRowSrc = CVPixelBufferGetBytesPerRowOfPlane(self, plane)
                let bytesPerRowDest = CVPixelBufferGetBytesPerRowOfPlane(copy, plane)

                if bytesPerRowSrc == bytesPerRowDest {
                    memcpy(dest, source, height * bytesPerRowSrc)
                }else {
                    var startOfRowSrc = source
                    var startOfRowDest = dest
                    for _ in 0..<height {
                        memcpy(startOfRowDest, startOfRowSrc, min(bytesPerRowSrc, bytesPerRowDest))
                        startOfRowSrc = startOfRowSrc?.advanced(by: bytesPerRowSrc)
                        startOfRowDest = startOfRowDest?.advanced(by: bytesPerRowDest)
                    }
                }
            }
        }
        return copy
    }
}

对 Swift 5 有效。提供更多背景知识......AVCaptureVideoDataOutput .videoSettings属性可以采用多种格式。并非所有人都有飞机，尤其是 ML 模型可能需要的飞机。

于 2019-10-31T16:27:23.323 回答
7

第二个实现看起来相当可靠。我能想象的唯一问题是新像素缓冲区中的一个平面被分配了不同的步长（每行字节数）。步长基于宽度×（每像素字节数），然后以未指定的方式四舍五入以实现最佳内存访问。

所以检查是否：

CVPixelBufferGetBytesPerRowOfPlane(self, plane) == CVPixelBufferGetBytesPerRowOfPlane(copy, plane

如果不是，则逐行复制像素平面：

for plane in 0 ..< CVPixelBufferGetPlaneCount(self)
{
    let dest            = CVPixelBufferGetBaseAddressOfPlane(copy, plane)
    let source          = CVPixelBufferGetBaseAddressOfPlane(self, plane)
    let height          = CVPixelBufferGetHeightOfPlane(self, plane)
    let bytesPerRowSrc  = CVPixelBufferGetBytesPerRowOfPlane(self, plane)
    let bytesPerRowDest = CVPixelBufferGetBytesPerRowOfPlane(copy, plane)

    if bytesPerRowSrc == bytesPerRowDest {
        memcpy(dest, source, height * bytesPerRowSrc)
    } else {
        var startOfRowSrc = source
        var startOfRowDest = dest
        for _ in 0..<height {
            memcpy(startOfRowDest, startOfRowSrc, min(bytesPerRowSrc, bytesPerRowDest))
            startOfRowSrc += bytesPerRowSrc
            startOfRowDest += bytesPerRowDest
        }
    }
}
于 2018-11-12T23:21:58.190 回答