When should I call CVPixelBufferLockBaseAddress and CVPixelBufferUnlockBaseAddress?
avfoundation, gpuimage, ios, opengl-es-2.0
Solution
You should lock each time you need to use it, and unlock when you are done and you don't need it anymore. This prevents the buffer from being overwritten, which can leave it in an inconsistent state. A firmware expert once explained this to me: in general, when handling video output, you should be mindful that there are many indirect references with pointers, which is like saying: "Hey it's mine, I'm using it, point to the next frame somewhere else". I can't tell based on your application when the buffer will no longer be needed, but that is something you should be able to figure out. If you had copied the buffer data somewhere else (such as creating a new object) it means that you could unlock it. Hope this helps.
Problem
In iOS6, I'm using OpenGL to do some rendering on AVFoundation video frames. I've seen a lot of example code that makes use of CVPixelBufferLockBaseAddress and CVPixelBufferUnlockBaseAddress, but it's unclear to me when exactly I perform the lock and unlock or why I'm doing it. Should I be locking the address when the CPU is modifying the memory? Or should I lock it when the GPU is reading from it? When should I unlock? Why would I ever even want to unlock? I've seen this Stack Overflow answer but it doesn't completely answer my question.