<iframe> should have a unique title attribute that identifies the content. The title will help screen reader users determine whether to explore the frame in detail. If an <iframe> contains no meaningful content, hide it by setting aria-hidden="true".
<iframe src="../welcome-video"></iframe><!-- good -->
<iframe src="../welcome-video" title="Welcome to GitHub Video" ></iframe><!-- also good -->
<iframe aria-hidden="true">
<!-- Meaningless JavaScript code -->
</iframe>