An embed code provides HTML markup that makes it possible to stream a YouTube video on an external Web page.

So it should use the HTML5 video if you have opted into YouTube's HTML5 trial. This will only be used for new articles, but I went ahead and re-published the article you linked.

Embedding YouTube in Dreamweaver. Dreamweaver embeds YouTube footage when you place the videos in inline frames. You don't need much knowledge of HTML code to create these frames. YouTube writes ...

VP9 video codec: YouTube’s implementation of HTML5 uses the VP9 codec, which Google says gives users higher quality video resolution with an average bandwidth reduction of 35 percent.