I'm always annoyed when I get to a website and it starts auto-playing some embedded video. Most of the time, I don't want to see the video, but rather the text of the story that got me to that site in the first place. It's even more annoying when, upon scrolling, the video reduces to a smaller window in the corner of the screen as it continues to play. In each of those case, I then have to mute, or pause, that video I don't want to watch.
I've recently come upon a solution that works, so I'm recommending it to you. It's an extension for the Chrome browser called "Disable HTML5 Autoplay." Unfortunately, there isn't a version for Safari or Internet Explorer, but it works great on Chrome. Note that it doesn't keep you from playing those videos -- you just have to hit play to get them rolling, even on YouTube.
Why do sites embed those auto-play videos in the first place? Because it helps them pump up the numbers they sell to advertisers. Even if you pause the video one second after it starts, that still counts as a view on the site's internal metrics. So, if a thousand people did that, none of them would have seen the content, but the site owner could convince advertisers that they did simply by showing them the stats. That would be like selling huge ratings for whatever show follows "The Big Bang Theory" because people left their TV or DVR going for five extra seconds after "TBBT" ended -- which would not be an accurate report on how many viewers that other show actually attracted.
I know of many radio stations that fool advertisers this way. They sell some business the sponsorship of all the video clips on the station's website, usually with a pre-roll commercial or embedded logo. The advertiser think it's getting tons of exposure, but most people don't watch the video and thus don't see the message. A friend at one station tells me that, as an experiment, they turned off auto-play on the whole site for a week, but when the number of views plunged, the sales manager made them turn it back on, even though she knew it was bogus information.
Even Facebook has been caught with incorrect data about video viewing metrics. The site now gives you an option to turn off auto-play, but I've seen a few get through in my timeline. Other sites do it much more blatantly, but I'm happy to say the "Disable HTML5 Autoplay" extension has stopped them all on my computer.
Let me know if it works for you -- and if you discover a similar extension for other browsers, send me a link so I can post that, too.