I would like to be able to know how much my eye tracking USB camera latency is. Which is before it is decoded and displayed on the LCD. Both take time, LCD alone may take 25 or more ms to show the frame.
A better method would be to have a Python camera lib that can tell when a new frame in a stream is ready and I could log that instead.
Not quite the answer to your question but a camera with very very low latency is the Sony playstation eye camera for the playstation 3. very good and cheaply available.
DirectShow driver for windows from internet archive here: