Get Download Link from Google Generated URL

i've been stuck on this error for over some days now. I have this app, that helps do some youtube conversion. I am using Youtube DL for the conversion, and after that, it generates a unique url in the form

https://r17---sn-p5qlsnl7.googlevideo.com/videoplayback?key=yt6&gir=yes&expire=1506012043&mt=1505990314&sparams=clen%2Cdur%2Cei%2Cgir%2Cid%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Crequiressl%2Csource%2Cexpire&pl=23&dur=727.741&lmt=1502263140756131&ip=54.147.55.117&ms=au&keepalive=yes&ei=K5fDWY3TFe6S8gSCjJnwBw&mv=u&source=youtube&id=o-AMxd1cK50iCKgEiy6DllYTFo-SeXUKSQ1fpmR3vdgsVa&mn=sn-p5qlsnl7&mm=31&signature=D5A495AD2061D93871BFDB91BF3843B061E5C73A.32EB5728DA132892E6CAA88581C77352DC6AC097&requiressl=yes&clen=10878177&itag=251&ipbits=0&mime=audio%2Fwebm&ratebypass=yes

The problem now is, the link above expires after 24 hours or less, and when i click on it, it takes me to a web browser with the media version, and when i click on download, it stores the file as videoplayback which at most cases does not play on using my pc's audio/video player.

How do i download the audio from the link directly, and also give it a unique name, instead of videoplayback..

Please help//