Replace video url with video player

Question

This is my plugin, this will replace the video shortcode format [video url="http://www.youtube.com/watch?v=sOnqjkJTMaA"][video] (Requirement is to show the video when a user placed a shortcode like this, in the Add New of admin. So I created this plugin with standard format http://www.youtube.com/watch?v=sOnqjkJTMaA.

<?php
/*
Plugin Name: My Plugin
*/
function video_url_format()
{
    $content = get_the_content();
    $pieces = explode('"', $content);
    return $pieces[1];

}
add_action('the_content','video_url_format');

?>

As you mention the WordPress will automatically show the videoplayer. But it will not show the player. If I paste a standard URL from YouTube like http://www.youtube.com/watch?v=sOnqjkJTMaA, it also doesn't show the video player. But if I commented out the line add_action('the_content','video_url_format'); in the plugin, then it will show the video player. So the problem may related to my plugin. Please make some point on it. Help please to complete it.

Answer 1

There appear to be a few problems with your plugin as written.

1. As mentioned in the comments above, WordPress has the built-in ability to automatically embed certain types of media, including YouTube videos, given a URL. See the Codex page on Embeds. So it's likely that your plugin isn't necessary, at least for a YouTube embed.
2. the_content is a filter hook, not an action hook. So typically you'd use add_filter() to filter the post's content.
3. Even if you were to attach your function to a proper action hook, you wouldn't see any output from it. Your function, as written, returns a variable, but add_action() ignores your return -- according to the Codex, add_action() always returns true.

Actions typically either echo() content to the screen (well, the response buffer) or modify a variable; Filters typically accept one or more variables, and return a (possibly modified) version of that variable. See this question for an in-depth look at the differences.