Something like:
Code:
a.youtube {
/*do not underline the link*/
text-decoration: none;
}
<a class="youtube" href="https://www.youtube.com/watch?v=-14SllPPLxY">
<img alt="image of youtube video" src="./Images/youtubevideo.png" />
</a>
I'm not sure that any level of Epub is guaranteed to support video playback.
In addition, the link may get opened in the ereaders browser (if it has one).