Yes, I am tinkering with the theme right now. I should be finished by the end of the week.
In the meantime, this is how I edited your $output
string:
$output = '<div class="fluid_8t" style="position:relative;padding:0;width:100%;padding-top:100%;margin-bottom:1.563em;">';
$output .= '<iframe class="nd-eight" src="https://8tracks.com/mixes/' . intval($xml->mix->id) . '/player_v3_universal/' . $playops .'" ';
$output .= 'width="' .intval( $width ) . '" height="' . intval( $height ) . '" style="border: 0px none;width:100%;height:100%;position:absolute;left:0;top:0;"></iframe>';
$output .= '</div>';
As you can see, though not wholly optimal, I am using inline styles to make the image responsive. I don’t know if you want to include that in your code or, as I was suggesting, allow themes to filter the $output
with something like this:
// allow plugins to filter the output
$output = apply_filters( 'eighttracks_shortcode', '', $atts );
if ( $output != '' ) return $output;
Just a thought. Still love the plugin though. It has actually gotten me excited about my 8tracks account again.