above-the-fold render time on WPT

At the Velocity Online Conference today, we announced the option to collect above-the-fold (AFT) render time on webpagetest.org (WPT). This is an option that runs in tandem with video capture to analyze screen shots to identify the time/frame at which browser window visible content is rendered.

To try this out for your web page, click the option on the Video tab at the bottom of Advanced Settings.

Download the presentation slides for background, heuristics, and WPT features for AFT.

Thanks to Zoe Abrams (algorithm design) and Pat Meenan (WPT integration).

Jake Brutlag

Hi Guys,

This looks absolutely fantastic, thanks so much.

Can this statistic be captured in the XML results from the Public Instances?

Also, is there, or could there be, a mechanism to capture and track this over time, possibly using WPTMonitor as we do now for start render and load time?


Awesome guys, well done Pat, Zoe and Jake!

It should already be exposed in the XML interface (probably as in the page data section). The XML dumps all of the data fields automatically. It should be easy enough to add as a metric to WptMonitor. Just be aware that measuring AFT is FREAKISHLY expensive because it has to capture 4 minutes of video. That means the test machines will each be tied up for 4 minutes per url being measured.

Does the http://code.google.com/p/webpagetest/ Google Code version support the AFT timing? I’m finding information on the AFT feature to be quite scarce.

Yes it does. The AFT logic is largely encompassed in a single class:
The Calculate method of the class is called from ~line 390 of PagetestReporting.cpp:

Has this now been removed from webpagetest?

Seems like this feature is no more present on WPT?

No. SpeedIndex has long-since eclipsed it as a better “above the fold” metric. There is also “visually complete” if you want something closer to the fully-complete AFT from before.