WordPress: Why does my Embed code / YouTube / Javascript disappear after I save a post?

Why Are All My Embed Codes Gone When I Save a WordPress Post?

WordPress has some security features built into it that won't allow you to add add Embed code to your page for videos, audio or other functions.

This applies to users who have one of these Roles:

• Author
• Contributor
• Editor

This does not apply to the Administrator -- which may cause some confusion because Embed codes will work fine for the Administrator but not other users.

How to Embed Video and Audio Content in WordPress

Actually, it's quite easy for most major sources of multimedia.

All you have to do is:

Insert the URL of  the Video / Audio source on its own separate line.

Example.

This is a paragraph. Blah, yadda, wah. Hey, check out this freaky dog video. 

https://www.youtube.com/watch?v=wRtHKb7-H5w 

This is another paragraph here. Wasn't that video funny?

With the latest version of Wordpress 4.0, you should automatically and immediately see the video in the visual editor. Checking the code will still only show the embed URL -- possibly with some paragraph tags around it, which is fine.

WordPress talks about this feature here, with a full list of services that work with emebeds:

Embeds: WordPress Codex

The 4.0 list includes these popular services:

• Animoto
• Blip
• CollegeHumor
• DailyMotion
• Flickr
• FunnyOrDie.com
• Hulu
• Imgur
• Instagram
• Issuu
• Meetup.com
• EmbedArticles
• Mixcloud
• Photobucket
• PollDaddy
• Rdio
• Revision3
• Scribd
• SlideShare
• SmugMug
• SoundCloud
• Spotify
• TED
• Twitter
• Vimeo
• WordPress.tv
• YouTube
• iSnare