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Chrome 66 rolls out: Autoplay video silenced by default plus 62 bugs fixed

Chrome 66 mutes audio on autoplay video by default unless a user tends to watch video on a site with sound on.

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Chrome 66 is out and, as Google promised last month, it will now block sound on autoplay content by default to reduce unexpected video playback with sound on the first visit.

The silencing feature has arrived two versions later than initially planned, but in the meantime Chrome users have been able to permanently block sound on a site-by-site basis.

Chrome will allow autoplay if the content is muted, or if the user has clicked on the site or previously shown interest in media on it.

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On Chrome desktop, Google is using the Media Engagement Index (MEI) to determine if the user has previously played video with sound on a site. On mobile, autoplay with sound will be allowed if the user has added the site to their home screen.

The MEI gauges users' tendency to consume media on a site and will allow sites to ignore the rule if the user's engagement passes a certain threshold.

This threshold is determined by the ratio of visits to "significant media playback events" on each site, which include measures such as whether audio and video consumption exceeds seven seconds, whether audio is present and unmuted, whether the tab with the video is active, and whether the size of the video is greater than 240 x 140 pixels.

Sites with a high score are those where users consume media regularly. Users can see the MEI by typing chrome://media-engagement into Chrome's address bar.

Google is using Chrome 66 to conduct a small trial of Site Isolation, which keeps pages from different websites in their own sandboxed processes to thwart attempts by malicious sites to steal data from other sites.

The feature has been available to manually enable since Chrome 63. Google also sees Site Isolation as an extra mitigation against Spectre attacks, but one of the trade-offs is that enabling Site Isolation in Chrome 65 bumped up memory usage by about 10 to 12 percent when isolating all sites with many tabs open.

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Chrome developers fixed several bugs in Site Isolation in Chrome 66 and this trial lays the foundation for a broader upcoming launch of the feature.

Chrome 66 also brings fixes for 62 security bugs, though 14 of the bugs didn't qualify for a cash reward. Google paid $34,000 to researchers who reported the bugs, with several rewards to be determined.

Additionally, Chrome 66 removes trust for digital certificates issued by Symantec's legacy PKI before June 2016. In Chrome 70, due out in stable release this October, all Symantec certificates will stop working and will display a certificate warning in the browser.

In Chrome 66 enterprise admins can temporarily remove Chrome's distrust of the Symantec PKI. However, this policy will expire after Chrome 73, which should be released in January 2019.

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