Animated pages and visual metrics

Hi, I am wondering how we should interpret visual metrics such as speed index when a page has lots of animations?

An example will be the Amazon home page (

They have a large image in the middle that auto scrolls. By looking at the video, I would say visual complete is at about 4s when the sign up button pops up. But because the big image keeps changing, the test considers the last frame to be at 14s. This means that the visual metrics are being overestimated. Is my understanding correct?

Yes you are correct. The page is mostly completed by 4 seconds, but the animation throws it off. At the 14 seconds is when the MP4 gamer glory begins to load.

See this info in the WPT documentation:

" This is the original mechanism that was used to calculate visual progress when the Speed Index was initially created and still works well but there are some cases where it has problems (video playing on pages, slideshows animating or large interstitials). It is very sensitive to the end state and calculates the progress based on the final image. It is also only measurable in a lab and relies on video capture being possible."