Does Postmatic render videos and embeds?
Postmatic does support the oEmbed standard and content in your posts that use oEmbed (or just the iframe or object tags) will render with a nice looking placeholder and the option to view that content in a browser. We even do a pretty good job of showing a proper placeholder depending on if it is a video, audio, or document.
Some oEmbed content actually renders just fine within an email so we let it. Two commonly used examples are embedded tweets as well as pages from Meetup.