How to embed a YouTube video into Markdown?

There are different ways to embed a YouTube video in Markdown documents.

If the Markdown processor supports inline HTML, a YouTube player can be embedded using an iframe:

<iframe
  width="640"
  height="480"
  src="https://www.youtube.com/embed/UmX4kyB2wfg"
  frameborder="0"
  allow="autoplay; encrypted-media"
  allowfullscreen
>
</iframe>

If the Markdown processor does not support inline HTML, the only way to add a video is to add an image that links to the video. You can use your own image or the thumbnail generated by YouTube. YouTube provides the following thumbnails for each video:

URL	Description
https://img.youtube.com/vi/VIDEO_ID/0.jpg	Full-size thumbnail
https://img.youtube.com/vi/VIDEO_ID/1.jpg, https://img.youtube.com/vi/VIDEO_ID/2.jpg, https://img.youtube.com/vi/VIDEO_ID/3.jpg	Small thumbnail images
https://img.youtube.com/vi/VIDEO_ID/default.jpg	Default thumbnail image
https://img.youtube.com/vi/VIDEO_ID/hqdefault.jpg	High-quality default thumbnail image
https://img.youtube.com/vi/VIDEO_ID/mqdefault.jpg	Medium-quality default thumbnail image
https://img.youtube.com/vi/VIDEO_ID/sddefault.jpg	Standard-definition default thumbnail image
https://img.youtube.com/vi/VIDEO_ID/maxresdefault.jpg	Maximum-resolution default thumbnail image

Additionally, i.ytimg.com can be used in place of img.youtube.com in all of the URLs listed above.

Using one of the thumbnails, it is possible to add a link with a still from a video, e.g.:

[![IMAGE_ALT](https://img.youtube.com/vi/UmX4kyB2wfg/0.jpg)](https://www.youtube.com/watch?v=UmX4kyB2wfg)

How to embed a YouTube video into Markdown?

See also