I have the same issue a few people have had with the Embed plugin, that embedded video's from YouTube do not present correctly at all by just applying the link.
They appear full width on the forum, but only maybe 150 pixels high!
As a workaround I have the settings to 600 px high & width to 0, but that breaks on a mobile phone & will not work for every-bodies different sizes of browsers on their screens.
If I make the setting 100% high, it does not work, it appears maybe 150 px high.
is the video.
Before you tell me to disable the YouTube plugin like you have everyone else, I don't have one!