[Coroner]

I've checked this out - and it works. See image !

Another way you can do, is:
open umg_extensions.php and search the following part:

	case 'mpg':
		$width  = $ext['mpg']['width'];
		$height = $ext['mpg']['height'];
		$url    = $media_url;
		$mtpl   = 'media';
		$mime   = 'video/x-mpeg';
		break;

change the width and high as you like, maybe:

	case 'mpg':
		$width  = 640;
		$height = 480;
		$url    = $media_url;
		$mtpl   = 'media';
		$mime   = 'video/x-mpeg';
		break;