Ok found a solution
function product_gallery_shortcode($atts) {
extract(shortcode_atts(array(
'product_id' => '31',
'prodvid' => false,
'youtubeids'=> '',
'thumbnr' =>2
), $atts));
etc
and i had to turn youtubeids into an array again
$youtubeidsnew = array();
$youtubeidsnew = explode(',', $youtubeids);