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>

The above code returns a URL like:

    http://example.com/files/528/Rabba_Ho_-_Falak_Shabir_Song.html.