Do something for every file in a directory

[helpmeplease2]

I am trying to make thumbnails from each .flv file using ffmpeg. I want a script to make the thumbnails. I am new to php and I am having trouble. I am using this currently, but its not making any thumbnails. ffmpeg does work by itself, so there is something wrong with my noobish PHP. I would also like to somehow remove the .flv extension and make it .jpg. Some help please?

<?php
$path = "videos";
$dir_handle = @opendir($path) or die("Unable to open $path");

while ($file = readdir($dir_handle))
{
   if($file!="." && $file!="..")
   exec("START c:/ffmpeg/ffmpeg -vcodec jpeg -i $file -ss  00:00:30 -vframes 1 images2/$file.jpg");
}
closedir($dir_handle);
?>