UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36

Steps to reproduce the problem:
1. Connect to headless chrome via devtools protocol
2. Call Page.startScreencast({everyNthFrame:2})
3. Load a page which triggers only one frame render per second
4. You only get frames every two seconds...

What is the expected behavior?
Replace everyNthFrame with maximumFramesPerSecond.

What went wrong?
everyNthFrame is just not useful in real world scenarios.

The only reason why you set this to >1 would be to increase performance at the cost of getting fewer frames back. This strategy makes sense assuming a constant and high framerate,  but the framerate is not constant and is entirely dependent on the content/activity of the page. 

Some pages will only cause one frame to render and in these cases you will never receive a frame for the page if everyNthFrame>=2. 

Similarly, if a page updates after a few seconds, but still only generates 1 new frame render, you may not see this frame at all.

Did this work before? No 

Chrome version: 65.0.3325.181  Channel: n/a
OS Version: OS X 10.12.6
Flash Version: 

Please add a maximumFramesPerSecond option to this feature.