1. On YouTube, go to the video you wish to embed.
2. Click Share, then Embed.
Copy the embed code
3. Choose your settings, then copy the HTML code.
4. In your BigCommerce control panel, open the page, product, or category you'd like to add the video to.
5. In the Page Content or Product Description editor, click the HTML icon in the toolbar.
HTML source button in the WYSIWYG editor
6. Paste the code, then add ?rel=0&autoplay=1 to the code. See the example below.
Before
<iframe width="640" height="360" src="[YouTube Video URL]" frameborder="0" allowfullscreen></iframe>
After
<iframe width="640" height="360" src="[YouTube Video URL]?rel=0&autoplay=1" frameborder="0" allowfullscreen></iframe>
7. Select Update.
The HTML Source editor with the Update button in the lower left highlighted
8. Save your changes before exiting.

Example: