Thanks for your answers! :)
By free format, I meant a format with an open specification, and by `same image quality` I was somewhat informal there :) but I won't bother you anymore with this. I was asking because I'm in the process of replacing everything I'm doing on the computer with free equivalents, and I guess I'll be using vp8 and vp9 as you suggested in order to convert my proprietary stuff, whenever possible(I already use Vorbis for audio, and it works like a charm). ;)
Thanks again!