Tag Archives: rendering

Googlebot evergreen rendering in our testing tools

Today we updated most of our testing tools so they are using the evergreen Chromium renderer. This affects our testing tools like the mobile-friendly test or the URL inspection tool in Search Console. In this post we look into what this means and what went into making this update happen.

The evergreen Chromium renderer

At Google I/O this year we were happy to announce the new evergreen Googlebot.

At its core the update is a switch from Chrome 41 as the rendering engine to the latest stable Chromium. Googlebot is now using the latest stable Chromium to run JavaScript and render pages. We will continue to update Googlebot along with the stable Chromium, hence we call it "evergreen".

Comparison between the rendering of a JS-powered website in the old and new Googlebot
A JavaScript-powered demo website staying blank in the old Googlebot but working fine in the new Googlebot.

What this means for your websites

We are very happy to bring the latest features of the web platform not only to Googlebot but to the tools that let you see what Googlebot sees as well. This means websites using ES6+, Web Components and 1000+ new web platform features are now rendered with the latest stable Chromium, both in Googlebot and our testing tools.
A comparison showing the old and the new mobile-friendly test. The old mobile-friendly test rendered a blank page and the new one renders the page correctly
While the previous version of the mobile-friendly test doesn't show the page content, the new version does.

What the update changes in our testing tools

Our testing tools reflect how Googlebot processes your pages as closely as possible. With the update to the new Googlebot, we had to update them to use the same renderer as Googlebot.

The change will affect the rendering within the following tools:
We tested these updates and based on the feedback we have switched the tools listed previously to the new evergreen Googlebot. A lot of the feedback came from Googlers and the community. Product Experts and Google Developer Experts helped us make sure the update works well.

Note: The new Googlebot still uses the same user agent as before the update. There will be more information about an update to the user agent in the near future. For now, Googlebot's user agent and the user agent used in the testing tools does not change.

We are excited about this update and are looking forward to your feedback and questions on Twitter, the webmaster forum or in our webmaster office hours.

Rendering AJAX-crawling pages

The AJAX crawling scheme was introduced as a way of making JavaScript-based webpages accessible to Googlebot, and we've previously announced our plans to turn it down. Over time, Google engineers have significantly improved rendering of JavaScript for Googlebot. Given these advances, in the second quarter of 2018, we'll be switching to rendering these pages on Google's side, rather than on requiring that sites do this themselves. In short, we'll no longer be using the AJAX crawling scheme.

As a reminder, the AJAX crawling scheme accepts pages with either a "#!" in the URL or a "fragment meta tag" on them, and then crawls them with an "?_escaped_fragment_=" in the URL. That escaped version needs to be a fully-rendered and/or equivalent version of the page, created by the website itself.

With this change, Googlebot will render the #! URL directly, making it unnecessary for the website owner to provide a rendered version of the page. We'll continue to support these URLs in our search results.

We expect that most AJAX-crawling websites won't see significant changes with this update. Webmasters can double-check their pages as detailed below, and we'll be sending notifications to any sites with potential issues.

If your site is currently using either #! URLs or the fragment meta tag, we recommend:

  • Verify ownership of the website in Google Search Console to gain access to the tools there, and to allow Google to notify you of any issues that might be found.
  • Test with Search Console's Fetch & Render. Compare the results of the #! URL and the escaped URL to see any differences. Do this for any significantly different part of the website. Check our developer documentation for more information on supported APIs, and see our debugging guide when needed.
  • Use Chrome's Inspect Element to confirm that links use "a" HTML elements and include a rel=nofollow where appropriate (for example, in user-generated content)
  • Use Chrome's Inspect Element to check the page's title and description meta tag, any robots meta tag, and other meta data. Also check that any structured data is available on the rendered page.
  • Content in Flash, Silverlight, or other plugin-based technologies needs to be converted to either JavaScript or "normal" HTML, if their content should be indexed in search.

We hope that this change makes it a bit easier for your website, and reduces the need to render pages on your end. Should you have any questions or comments, feel free to drop by our webmaster help forums, or to join our JavaScript sites working group.

Smoother <video> in Chrome

Video quality matters, and when an HD or HFR playback isn’t smooth, we notice. Chrome noticed. YouTube noticed. So we got together to make YouTube video playback smoother in Chrome, and we call it Project Butter.

For some context, our brains fill in the motion in between frames if each frame is onscreen the same amount of time - this is called motion interpolation. In other words, a 30 frames per second video won’t appear smooth unless each frame is spaced evenly each 1/30th of a second. Smoothness is more complicated than just this - you can read more about it in this article by Michael Abrash at Valve.

Frame rates, display refresh rates and cadence
Your device’s screen redraws itself at a certain frame rate. Videos present frames at a certain rate. These rates are often not the same. At YouTube we commonly see videos authored at 24, 25, 29.97, 30, 48, 50, 59.94, and 60 frames per second (fps) and these videos are viewed on displays with different refresh rates - the most common being 50Hz (Europe) and 60Hz (USA).  

For a video to be smooth we need to figure out the best, most regular way to display the frames - the best cadence. The ideal cadence is calculated as the ratio of the display rate to frame rate. For example, if we have a 60Hz display (a 1/60 second display interval) and a 30 fps clip, 60 / 30 == 2 which means each video frame should be displayed for two display intervals of total duration 2 * 1/60 second.

We played videos a bunch of different ways and scored them on smoothness.  

Smoothness score
Using off the shelf HDMI capture hardware and some special video clips we computed a percentage score based on the number of times each video frame was displayed relative to a calculated optimal display count. The higher the score, the more frames aligned with the optimal display frequency. Below is a figure showing how Chrome 43 performed when playing a 30fps clip back on a 60Hz display:

Smoothness: 68.49%, ~Dropped: 5 / 900 (0.555556%)

The y-axis is the number of times each frame was displayed, while the x-axis is the frame number. As mentioned previously the calculated ideal display count for a 30fps clip on a 60Hz display is 2. So, in an ideal situation, the graph should be a flat horizontal line at 2, yet Chrome dropped many frames and displayed certain frames for as many as 4 display cycles! The smoothness score reflects this -  only 68.49 percent of frames were displayed correctly. How could we track down what was going on?

Using some of the performance tracing tools built into Chrome, we identified timing issues inherent to the existing design for video rendering as the culprit. These issues resulted in both missed and irregular video frames on a regular basis.

There were two main problems in the interactions between Chrome’s compositor (responsible for drawing frames) and its media pipeline (responsible for generating frames) --  
  1. The compositor didn’t have a timely way of knowing when a video frame needed display. Video frames were selected on the media pipeline thread while the compositor would occasionally come along looking for them on the compositor thread, but if the compositor thread was busy it wouldn’t get the notification on time.
  2. Chrome’s media pipeline didn’t know when the compositor would be ready to draw its next new frame. This led to the media pipeline sometimes picking a frame that was too old by the time the compositor displayed it.

In Chrome 44, we re-architected the media and compositor pipelines to communicate carefully about the intent to generate and display. Additionally, we also improved which video frames to pick by using the optimal display count information. With these changes, Chrome 44 significantly improved on smoothness scores across all video frame rates and display refresh rates:
Smoothness: 99.33%, ~Dropped: 0 / 900 (0.000000%)

Smooth like butter. Read more in public design document, if you’re interested in further details.

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