Directshow,capture two USB webcams, can't start at same time

I have two graph in开发者_运维问答 my program each one can control a USB camera to capture video data.

I can start them separately without problem like:

cam_a.start();
sleep(100);
cam_b.start();

However,without the "sleep" the second graph will not execute correctly,like no file writing and no frame display.

Anyone can help to solve this problem?

Win7 64 bits, windows sdk 7 Logitech c210 webcam Logitech c510 webcam Directshow video capture.

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In Windows Logitech USB Cams were usually TWAIN/WIA based (http://www.twain.org, http://msdn.microsoft.com/en-us/library/ms630368%28v=vs.85%29.aspx). Your issue is probably caused by the Logitech TWAIN/WIA driver not being thread safe or having a bug. Your DV-1394 Cam probably uses a diferent driver so there is no colision with the Logitech driver.