Markdown Image Tags as YouTube and Embed Blocks

In markdown, an image tag look something like this when you want to drop it into a document.

![alt text](https://example.com/image.jpg)

For my projects, I don’t think of these tags strictly as images, but rather blocks of content with an image representation. In practice, that means I want to embed YouTube vidoes in my content pages like this:

![YouTube video update of my Phlex on Rails course](https://youtu.be/20TEOGOtXTY)

Out of the box this wouldn’t work, but fortunately since I use the Markdown Rails gem, I can intercept image tags and process them as blocks of content. Here’s what my Markdown parser looks like in my application.

class ApplicationMarkdown < MarkdownRails::Renderer::Rails
  # Process markdown image blocks
  def image(link, title, alt)
    url = URI(link)
    case url.host
    when "youtu.be"
      youtube_tag url, alt
    else
      super
    end
  end

  # ...

  private
    # This is provided as an example; there's many more YouTube URLs that this wouldn't catch.
    def youtube_tag(url, alt)
      <<~HTML
        <iframe
          class="aspect-video w-full rounded"
          src="https://www.youtube-nocookie.com/embed#{url.path}"
          title="YouTube video player"
          frameborder="0"
          allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share"
          referrerpolicy="strict-origin-when-cross-origin"
          allowfullscreen
        ></iframe>
      HTML
    end
end

When I stack it all up and publish the content, I see a YouTube embed.

See it live in the Phlex on Rails: Week One Update article.