public function thumb($size, $start, $videoFrames = 1)
{
//$input = false;
if (!is_numeric($videoFrames) or $videoFrames <= 0) {
$videoFrames = 1;
}
$this->audioDisable();
$this->size($size);
$this->position($start);
$this->videoFrames($videoFrames);
$this->frameRate(1);
return $this;
}