Issue confirmed on my site as well. We should probably also consider HTML5 Youtube embedding, if that's possible. I noticed it still uses Flash on Composr. But that's a separate issue.

Naughty Google. They do seem to have dropped it, which is really bad given that there's a decade of people using their embed code to link stuff into blogs etc.
Maybe it's an unintended bug on their end.

We should move to the HTML5 player though, so a fix will come shortly.