First sorry about my bad english. I use this in my PHP apps links:
<?php $theURL = "http://example.com/files/528/Rabba Ho - Falak Shabir Song.html"; ?>
<a href="<?= str_replace( " ", "_", $theURL ); ?>" target="_blank">
Rabba Ho - Falak Shabir Song
</a>
EDIT: Sorry for last error, i edit now...
The above code returns a URL like:
http://example.com/files/528/Rabba_Ho_-_Falak_Shabir_Song.html.