Convert all youtube link to embed

EDIT

After reviewing your edit, you may want to try following These Instructions

To embed a video or another object into a post or page, place its URL into the content area. Make sure the URL is on its own line and not hyperlinked (clickable when viewing the post).

It sounds like you would want to use wp_get_oembed() - The examples look like this:

Retrieve the embed code for a URL from a supported oEmbed provider:

<?php $embed_code = wp_oembed_get('http://www.youtube.com/watch?v=tkEvSjdDfiA'); ?> 

Retrieve the embed code for a URL from a supported oEmbed provider - with width argument:

<?php $embed_code = wp_oembed_get('http://www.youtube.com/watch?v=tkEvSjdDfiA', array('width'=>400)); ?> 

If that doesn't work you could probably apply 'the_content' filter:

apply_filters( 'the_content', 'http://www.youtube.com/watch?v=tkEvSjdDfiA' ); 

But that filter is probably overkill for what you're trying to achieve.

When you enter the URL, put your editor in TEXT mode. Lots of people don't notice the visual editor converts HTML special characters, and deactivates links.

You are making wrong use of the the_content filter.

Why your code is not working

• You are not returning anything back to the referenced content

• Even if your condition fails, you should pass the referenced content back, otherwise nothing will be displayed if your condition returns false

• Your preg_match function is using the wrong subject. Use the referenced content here. (This is just a note, you don't need to call the global $post)

• Your pattern is also wrong, it does not match any pattern thus failing and returning the content as-is

With the current code that you have, I have gone with parse_url() and parse_str() thanks to this answer. It has to be noted that from your original question that you are using the following format

• http://www.youtube.com/watch?v=C4kxS1ksqtw&feature=related and
• http://www.youtube.com/watch?v=C4kxS1ksqtw.

This code only works on the format watch?v=

I have modified your code accordingly:

add_filter('the_content', function ($post_content) { parse_str( parse_url( $post_content, PHP_URL_QUERY ), $matches); if (!empty($matches['v'])) { $post_content = '<object width="415" height="250">'; $post_content .= '<param name="movie" value="http://www.youtube.com/v/' . $matches['v'] . '&hl=en_US&fs=1&"></param>'; $post_content .= '<param name="allowFullScreen" value="true"></param>'; $post_content .= '<param name="allowscriptaccess" value="always"></param>'; $post_content .= '<embed src="http://www.youtube.com/v/' . $matches['v'] . '&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="415" height="250"></embed>'; $post_content .= '</object>'; $post_content = $post_content; } return $post_content; }); 

EDIT

As a test, the following code

<?php $string = 'http://www.youtube.com/watch?v=C4kxS1ksqtw&feature=related'; parse_str( parse_url( $string, PHP_URL_QUERY ), $matches); ?><pre><?php var_dump($matches); ?></pre><?php 

gives the following output when dumped

array(2) { ["v"]=> string(11) "C4kxS1ksqtw" ["feature"]=> string(7) "related" }