Reference:
a descriptive title attribute value is not required for accessibility, but if the inline frame presents content as a whole that is visually distinctive, such as an advertisement or video player, then a title should be provided to indicate this distinction.<iframe src="https://www.youtube.com/embed/66L2e5Jtzag?rel=0" title="Message from Department Chair Tim Fisher" width="560" height="315" frameborder="0"></iframe>
Because many users enlarge fonts and other page elements to increase visibility and accessibility, you should not disable scrolling for iframes (or frames, for that matter) by using scrolling="no". The default scrolling value (auto) is usually the best option. You should also, when possible, design the iframe with relative sizes so the iframe element itself will scale as the page and its contents are resized.
In order to solve the "Inline frame without a text alternative" issue, please use the embed code instead of pasting the video URL.
How to embed a video: https://support.google.com/youtube/answer/171780?hl=en
Updated