Sample Grabber hangs on repeated VFW_E_WRONG_STATE

[jaraco]

Originally reported by: Jason R. Coombs (Bitbucket: jaraco, GitHub: jaraco)

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In testing the grabber on my virtual machine connected to a Microsoft Lifecam, I find that the simple save_frame operation just hangs. It's caught in an infinite loop, repeatedly receiving VFW_E_WRONG_STATE on the call to GetCurrentBuffer.

According to this reference, polling the buffer may not be a reliable technique for getting frames, and it might be necessary to write a callback.

help needed

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• Bitbucket: https://bitbucket.org/jaraco/jaraco.video/issue/7