Are you just caching a preview? You shouldn't try to cache a whole song at once. AE is not made for long playback. What, exact, version of AE are you using? If you want to watch the whole thing, I recommend rendering out via the Render Queue or the Adobe Media Encoder.
I have the newest Adober After Affects and I rendering a spectrum video I've made thats 3 minutes long, it took 8 hours to render and download as a 12 GB file.
Some things take a while to render. What resolution were you rendering? Did you have your composition set to use the ray-traced renderer or the classic renderer?
The resulting file should be large - that's expected (depending on your render settings). I usually render from AE, then take the resulting file into Adobe Media Encoder to make my final deliverable (the Adobe Media Encoder even has presets for YouTube, Vimeo, Facebook, etc.)