Printing OEmbed URL based on Post selected w/o page refresh

wp_oembed_get() returns the whole iframe, that’s its purpose. So you should use it on its own, not in the src of an iframe.

$url = esc_url( get_post_meta( get_the_ID(), 'video_oembed', 1 ) ); 
echo wp_oembed_get( $url );

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