Markdown supports HTML, so if you need to, say, embed a YouTube video, you can just copy and paste the embed code from them, drop it into a Markdown document, and you should be good to go. With YouTube specifically, there are other options. But in general, you don’t need to do anything special to embed third-party media in Markdown.
You do need to do whatever is necessary for that particular service though. For example, on CodePen, you visit any particular Pen to get the embed code, click “Embed” in the footer, choose options, and ultimately get the embed code. On Twitter, you click a down arrow thingy and choose Embed Tweet, then get forwarded to some other website where you choose options and ultimately get the embed code. It’s different on every service.
That’s the spirit behind gatsby-remark-embedder from Michaël De Boey, which I recently saw. It spells this out:
Trying to embed well known services (like CodePen, CodeSandbox, Slides, SoundCloud, Spotify, Twitter or YouTube) into your Gatsby website can be hard, since you have to know how this needs to be done for all of these different services.
So what this plugin does is allows you to drop a URL to the thing you’re trying to embed on its own line, and it’s magically transformed into embed code. For example, you put a URL to a Pen like this:
…and you get:
<iframe src="https://codepen.io/team/codepen/embed/preview/PNaGbb" style="width:100%; height:300px;" ></iframe>
…by the time the content makes its way to the DOM.
What I think is a smidge funny is that… this is exactly what oEmbed is. The whole spirit of oEmbed is, “Put a URL to a thing on its own line and we’ll try to make it into an embed for you.” It’s a clearly defined spec and there is a clear source of data of sites that support the feature.
But I suppose it’s a failing of oEmbed that people either don’t know about it or don’t use it. Even Embedly seems kinda dead-ish?