screen captures, how is frame rate sync'ed during capturing?

[vhelp]

hi all

this one has me stumped. i've searched and searched but still can't find anything to help me. perhaps my search terms are way off. anyway. i'm coding my own screen capture app, so far so good. but what is killing me is the inaccurate timings when reading the screen. i can't seem to figure on a "lock" method to extract the unique frames from the screen, whether the video is from a webpage, virtualdub or tv card output window. i lock onto each windows by its handle for the video's rect. to keep things simple, i am using a small 352x240 dimension using virtualdub as my test tool for capturing the screen video as it plays. i prepped several videos (avisynth, ivtc short clip to 24p) to display a frame number for each image.

the issue is, when i capture the screen (video playing) there are many duplicates or drops. i can't seem to get the screen capture app to capture at 29.970 fps.

i'm not interested in already made screen capture apps.

this is a hobby of mine. plus, its something is started many years ago but gave up on because of the same issue--locking to a frame rate during screen capture.

thanks in advance for any leads.


* this is the test window i use in debugging with my screen capture app, delphi 6 code.

[vhelp]

well, just reporting on the apps progress...

so far, i've improved on my screen capture algo routine. just a few drops of frames here and there, though not as noticeable when capturing streaming video since they mostly lag here and there and the change are different every reload anyway, so the drops aren't as serious. so i'm getting closer to a capture/sync solution.