Its normal practise to embed youtube videos into a joomla article
1. Install "AllVideos - Joomla! Extensions Directory"
2. In your plugins manager >> edit the tinyMCE editor plugin as follow
Code Cleanup on Startup Off On
Code cleanup on save Never Front Only. Always
Do not clean HTML entities. Yes No
Save Warning Off On
Compressed Version Off On
3. add a you tube video into your content:
Copy the embedded video url from youtube
Go to Joomla article creation - Click the “html” icon on the tool bar.
Paste your “Video” code in the source code.
Click update and save the article.
In this way the video will be embedded to your article content.