CVPixelBufferLockBaseAddress为什么？使用AVFoundation捕获静止图像

我正在编写一个iPhone应用程序，使用AVFoundation从相机创建静态图像。
阅读编程指南我发现了一个几乎我需要做的代码，所以我试图逆向工程并理解它。

我遇到了一些困难理解将CMSampleBuffer转换为图像的部分。

所以这是我理解的，后来是代码。

CMSampleBuffer代表内存中的缓冲区存储其他数据。后来我调用函数CMSampleBufferGetImageBuffer（）只用图像数据接收CVImageBuffer。

现在有一个我不理解的函数，我只能想象它的函数：CVPixelBufferLockBaseAddress（imageBuffer， 0）;我无法理解它是否是一个线程锁，以避免对它进行多次操作或锁定缓冲区的地址，以避免在操作期间发生变化（为什么要更改？...另一帧，不是数据被复制在另一个地方？）。剩下的代码对我来说很清楚。

试图在google上搜索，但仍然没有找到任何帮助。

有人可以带点光吗？

I'm writing an iPhone app that creates still images from the camera using AVFoundation. Reading the programming guide I've found a code that does almost I need to do, so I'm trying to "reverse engineering" and understand it.
I'm founding some difficulties to understand the part that converts a CMSampleBuffer into an image.
So here is what I understood and later the code.
The CMSampleBuffer represent a buffer in the memory where the image with additional data is stored. Later I call the function CMSampleBufferGetImageBuffer() to receive a CVImageBuffer back with just the image data.
Now there is a function that I didn't understand and I can only imagine its function: CVPixelBufferLockBaseAddress(imageBuffer, 0); I can't understand if it is a "thread lock" to avoid multiple operation on it or a lock to the address of the buffer to avoid changes during operation(and why should it change?..another frame, aren't data copied in another location?). The rest of the code it's clear to me.
Tried to search on google but still didn't find nothing helpful.
Can someone bring some light?

-(UIImage*) getUIImageFromBuffer:(CMSampleBufferRef) sampleBuffer{

// Get a CMSampleBuffer's Core Video image buffer for the media data
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 

// Lock the base address of the pixel buffer 
CVPixelBufferLockBaseAddress(imageBuffer, 0); 

void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); 

// Get the number of bytes per row for the pixel buffer
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
// Get the pixel buffer width and height
size_t width = CVPixelBufferGetWidth(imageBuffer); 
size_t height = CVPixelBufferGetHeight(imageBuffer); 

// Create a device-dependent RGB color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 

// Create a bitmap graphics context with the sample buffer data
CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, 
bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
// Create a Quartz image from the pixel data in the bitmap graphics context
CGImageRef quartzImage = CGBitmapContextCreateImage(context); 
// Unlock the pixel buffer
CVPixelBufferUnlockBaseAddress(imageBuffer,0);

// Free up the context and color space
CGContextRelease(context); 
CGColorSpaceRelease(colorSpace);

// Create an image object from the Quartz image
UIImage *image = [UIImage imageWithCGImage:quartzImage];

// Release the Quartz image
CGImageRelease(quartzImage);

return (image);
}

谢谢，
Andrea

Thanks, Andrea