Flash playable video formata with php

Hi

I have a php script that handles the upload of files and want people uplodaing video put video thats compatible with flash player.

$name=$_FILES['vidfile']['name'];
$type=$_FILES['vidfile']['type'];
$size=$_FILES['vidfile']['size'];
$temp=$_FILES['vidfile']['tmp_name'];
$error=$_FILES['vidfile']['error'];

//This is suppose to check the type of vid file upload. I need all the vid  types to be flash compatible when access through xml

if($type=="vidfile/swf")

{

//okay to upload.

}

else

{

//not okay to upload.

}

The question is what file or video types will play on flash through xml and how can a verify any one uploading video has video in this format.

The last question is how do I create thumb nails of the uploaded videos. Like a clickable image of the thing some will watch thanx.