How to achieve smooth frame capture?

Question

Qt

Hello.
There is a program that captures frames from the monitor area, compresses them and writes them to avi:

char* frame = getFrame(); // Выполняется быстро
compress(frame); // Выполняется медленно
writeFrame(aviFile, frame);

The problem is that you need to do this with a given fps, but frame processing takes a significant amount of time (performed on the CPU) and fps is not respected. Please advise how to solve this problem?
PS:
For example, there is an option with frame buffering. Raw frames are first written to a buffer in RAM with a given fps. Frame processing and saving is performed in a separate thread. Thus, we achieve the desired smoothness at the cost of RAM and CPU consumption. Can you give me some advice on how best to implement this? Or share a link to an article/example?
Or the second option (weakly believe in it) is similar to the first: run the compress and writeFrame functions asynchronously using QtConcurrent::run. This is easier to implement, but how will it work? Will there be too many threads? Will there be a conflict when writing to a file?

Answer 1

Frame capture, in my opinion, is best done the old fashioned way - using Bitblt . In the main stream or not to capture - it's up to you. But I highly recommend saving frames and, moreover, processing them in a separate thread so as not to affect FPS.
And so that you, inadvertently, do not pile up any functions of "compressing" the image, I pay special attention to the fact that Bitblt can change the size of the image during the capture process, as well as the color format.