View Full Version : callback frame rate

January 26, 2004, 09:47:29
Hi Everyone

I'm using Grabber::addListener function for recieving callbacks when a frame is ready , but the callback seems to be called in 30 milliseconds and sometimes less , but isn't the hardware limited to 25 fps ?

Stefan Geissler
January 27, 2004, 07:45:32

The callback frequency depends on different issues.
1. The frame rate of the video capture device.
2. The CPU load: If your image processing in the frameReady() method takes more time than the frame rate uses per frame, the frameReady() method is not called for every delivered frame. Please refer to the callback sample, to see, what happens in this case.

Also there yould be an inaccuracy of the used timer. For timing purposes you can use the QueryPerformanceCounter() or the graph time, that is specified in the sample decription of the MemBuffer object. T

The time span between frameReady() calls should be 40 milliseconds at 25 frames per second on a real time operating system. Windows is no real time operating system, therefore this time span can dither. The average time span should accord to the frame rate.