baseAddress
是一个不安全的可变指针,更准确地说是UnsafeMutablePointer<Void>
。一旦将指针从Void
转换为更具体的类型,您就可以轻松访问内存:
// Convert the base address to a safe pointer of the appropriate type
let byteBuffer = UnsafeMutablePointer<UInt8>(baseAddress)
// read the data (returns value of type UInt8)
let firstByte = byteBuffer[0]
// write data
byteBuffer[3] = 90
确保使用正确的类型(8、16或32位无符号整数),这取决于视频格式。最可能是8位。
缓冲区格式更新:
您可以在初始化AVCaptureVideoDataOutput
实例时指定格式。基本上,您有以下选择:
- BGRA:单个平面,其中蓝色、绿色、红色和 Alpha 值分别存储在 32 位整数中
- 420YpCbCr8BiPlanarFullRange:两个平面,第一个平面包含每个像素的 Y(亮度)值的字节,第二个平面包含用于一组像素的 Cb 和 Cr(色度)值
- 420YpCbCr8BiPlanarVideoRange:与420YpCbCr8BiPlanarFullRange相同,但Y值限制在16-235范围内(由于历史原因)
如果您对颜色值感兴趣并且速度(或最大帧率)不是问题,则选择更简单的BGRA格式。否则,选择更高效的本机视频格式之一。
如果有两个平面,则必须获取所需平面的基址(请参见视频格式示例):
视频格式示例
let pixelBuffer: CVPixelBufferRef = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(pixelBuffer, 0)
let baseAddress = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0)
let bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 0)
let byteBuffer = UnsafeMutablePointer<UInt8>(baseAddress)
// Get luma value for pixel (43, 17)
let luma = byteBuffer[17 * bytesPerRow + 43]
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)
BGRA示例
let pixelBuffer: CVPixelBufferRef = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(pixelBuffer, 0)
let baseAddress = CVPixelBufferGetBaseAddress(pixelBuffer)
let int32PerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
let int32Buffer = UnsafeMutablePointer<UInt32>(baseAddress)
// Get BGRA value for pixel (43, 17)
let luma = int32Buffer[17 * int32PerRow + 43]
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)