It is built on top of Steem Blockchain. :) I'm giving you this advice, because you never know when your content can be banned on other platforms. There is a monthly fee (equivalent of about 3.5usd), but I think it's a good thing as it helps to prevent some users from spamming the system. I would be more than happy to help you with the first payment if you want. :)

There is also http://d.tube. It is built on top of Steem Blockchain too. It is older and better known than 3Speak, but the uploading process can be irritating, sometimes videos do not load. If you need anything, just ask me in the comment section under one of my posts. :)

When you upload something on any of those, they appear on Steemit.com automatically. Have a nice day!