Chrome Flash Shockwave File
Chrome has implemented some strict security that may prevent embedded website's YouTube videos from playing on auto-load. If you have Google's Chrome Canary and visit some websites, you may find that a mystery file gets downloaded.
If you open the mystery file in BBEdit, you may find the following:
Notice that the file starts with CWS. This indicates that the downloaded file is a Flash Shockwave file. This Shockwave file format is no longer being supported by Chrome, and other browsers may soon follow.
Why did the file get downloaded?
Chrome doesn't know what to do with the file, so instead of playing it, the file gets downloaded.
Ignoring the file, instead of downloading would have been a been a better solution.
You can get some additional background information from user kryptkat over on programming.com tech board:
https://cboard.cprogramming.com/tech-board/126640-cws-youtube-problem.html
Quick Solution for Web Developers
If this is happening to files on your website. You are probably using an old Embedded link to YouTube. The easy solution is to get the latest Embed URL from YouTube.
If your using YouTube anyplace on your website, you should download Chrome's Canary and browse your site.
Google Canary is Google's Developer Browser, it contains the latest and great code base that developers are testing before it become in the mainstream Google Chrome browser.