Aug. 4, 2014 Update | Twitter has been fixed, Bandcamp added. If any of these features stops working, feel free to send a message to ST Bot.
Soundcloud. There's a Soundcloud icon on the post page. Click it, paste your Soundcloud URL in the small window that opens, and your Soundcloud player will embed.
Youtube. Paste Youtube.com and Youtu.be URLs in the post page (with no extra tags) and the video should automatically embed.