GGPChat

Step 1:
Copy Youtube video code.

Click the Share text below the video, on the Youtube page of the video you wish to share:
Step 2:

Then select the code that appears after the URL and click the copy button.
Step 3:

Click the the Youtube button above the text box of your post. This paste a HTML tag into the text box used for posting -

[youtube][/youtube]
Step 4:

Place the cursor in between the HTML tags and paste the code.

Click Preview to check, and if good, click submit.