in your code
I dont understand why you have 2 hidden variables
then put same variables in your action link
those in link can be removed, they serve no real purpose
this version will work the same
<form action="" method="get">
<input type="text" name="tag">
<input type="hidden" name="action" value="index">
<input type="hidden" name="type" value="videos">
<input type="submit" value="GO">
</form>