To have a video Autoplay, you will need to place the thing below into 'Source'. You should keep in mind, that this isn't exactly a good thing to do on a forum. The part with 'Width="0" and Height="0" both determine the size of the clip. With both 0's, it will be essentially invisible. Then the URL is after that in bold.
HTML Code for Autoplay: <iframe width="0" height="0" src="//www.youtube.com/embed/BBBmI_-gscs?list=UUkiXOKnkDO4qz3njQoz86LA?rel=0&autoplay=1" frameborder="0" allowfullscreen></iframe>
This is for normal embedding. Everything is the same but it won't autoplay, so people will need to actually click the video for it to play.
HTML for embed videos: <iframe id="framecizgifilmuploads0" src="PUT URL HERE!" width="530" height="410" frameborder="0" scrolling="no" class="DRAGDIS_iframe"></iframe>
Genrally, by right clicking a video, it will give you the Embed code anyway.
If you want to test any of this, I recommend going to : http://www.w3schools.com/html/tryit.asp?filename=tryhtml_intro