Tbh, you can probably stick to using SC cause you'll be more likely to get listens and subs (at least that's been my experience) and you also get the added bonus of if your work isn't well received, listeners will more than likely just skip and you don't get a negative rating like with YT. If you absolutely must build a YT audience, then there are sites such as
http://www.clipconverter.cc/ which converts YT videos. Keep in mind, you'll still need software to add the cover you made to the video. At the most basic, there's Windows Movie Maker or AviUtil (both are free), but more complex software (for subs, layers, effects, etc.) are more than likely to be proprietary (tho I've heard that AviUtil can do some complex things, I haven't used it fully myself).