Using Yuto's latest part as an example.
If you just copy and paste a youtube link it might look something like this:
Link:https://www.youtube.com/watch?v=cW9OABECQkU&t=13s
To embed, take out everything after the "&" sign as well as the "s" after "http."
"http
s://www.youtube.com/watch?v=cW9OABECQkU
&t=13s"
becomes
Link:http://www.youtube.com/watch?v=cW9OABECQkU
Note: The "preview" button on the "post message" page doesn't work. If you can't get the preview to load, that's okay. Just hit "post" and if you've taken out the "s" and the extemporaneous stuff after the "&" sign in the video link you are golden.
http://www.youtube.com/watch?v=cW9OABECQkU