embed_oembed_html filter needs post ID

[filosofo]

If you want to use the embed_oembed_html filter in the context of a particular post, currently you have to hope that the global request variable stars align in your favor. That is, you have to hope that the shortcode callback---in which the filter is used---is being called in the admin when $_GET['post'] is defined. Because it's a shortcode callback, that's not something you can have great confidence in.

Patch passes the post ID to the filter.

[markjaquith]

(In [16740]) Pass post ID to embed_oembed_html filter to avoid global variable incantations. props filosofo. fixes #15491