Searching for alternative GIF-thumbnail file format: PNG

hello, the plugin works fine, thank you.

but in order of solving a custom design/layout problem I needed to have thought it would be nice to have the plugin generating a PNG-file (instead of the JPEG) as thumbnail due to the transparency.
By replacing the term jpeg into png in the gif-player.php, it first had the desired effect, but unfortunately now the play button (link)/the animation is not working any more.
sorry, I’m new to this css, html stuff… anyone helps me?