Please read your code carefully. I used your code, but changed the width and height.
function rezzz_embed_defaults($defaults) { $defaults['width'] = 540; $defaults['height'] = 304; return $defaults; } add_filter('embed_defaults','rezzz_embed_defaults');
You need to provide the width and height in the right ratio for using videos from youtube, vimeo and another source.
You can see a working demo of the above code here
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