Go back and check the code, it could be you placed a-  instead of a =  when you posted in.

something is wrong in what you added to the  code.

i have done that myself and had to go back and make changes.

Not sure of a player but to put on a autoplay video here are the directions.

Go to YouTube and find the video you want

1. under that video click on the word share

 2. on the left under where it says share click on embed .

3. a box comes up with video on the left and code is on  the right.

4. copy that code so you can paste to your page.

5.after you paste see this in front  <iframe      only change the iframe word to  embed

6. See on bottom this word  iframe>   again only change the word ony iframe to embed

7.  Go back to code . under the size  see where the code begins with http

look through that code till you see a ?

8. after that ?  add         &autoplay=1&       

9.

make sure you didn't make spaces      . save ,go look it's on your page as auto play