YouTube iframe embed not starting in HD

Question

I'm trying to embed an HD YouTube video but no matter what I try, it only ever seems to load the 480p version.

According to YouTube, embedding an HD video is as simple as adding hd=1 to the URL:

<iframe src="//www.youtube.com/embed/{videoId}?hd=1" width="960" height="720"  frameborder="0" allowfullscreen></iframe>

This, however, does not seem to be working, at least in my implementation of the iframe:

<iframe id="video-player" width="960" height="720" src="//www.youtube.com/embed/{videoId}?enablejsapi=1&autoplay=1&rel=0&modestbranding=1&showinfo=0&showsearch=0" frameborder="0" allowfullscreen></iframe>

The same is true with the Javascript API:

HTML:

<div id="video-player"></div>

JS:

    var player;
    function onYouTubePlayerAPIReady() {
        player = new YT.Player('video-player', {
            height: '720',
            width: '960',
            videoId: '{videoId}',
            playerVars: {
                'controls': 1,
                'autoplay': 1,
                'hd': 1
            },
            events: {
                'onReady': onPlayerReady,
                'onStateChange': onPlayerStateChange
            }
        });
    }

    function onPlayerReady(event) {
        player.playVideo();
    }

Answer 1

Use this parameter:

vq=hd1080

Example:

<iframe src="https://www.youtube-nocookie.com/embed/SzTdgE04uA8?vq=hd1080" width="853" height="480"></iframe>