/**
 *
 * Filter videojs player tag output, before player rendered.
 *
 * @param string $player
 * @param array $setup
 * @param string|int $source
 *
 */
add_filter( 'streamtube/player/file/output', function( $player, $setup, $source ){

    // Enqueue some JS/CSS ... etc

    if( wp_attachment_is( 'video', $source ) ){

        $player = 'Your custom player tag goes here';
    }

    return $player;

}, 100, 3 );