Hi and welcome.
Without exception, quality is always lost when doing any converting. You can apply noise reduction or other plugins that may mask quality issues, but the simple fact is that there is absolutely no way to increase quality. It just simply does not exist.
All codecs are lossy. The only video format that is not is uncompressed RGB. There is an exception to this in the video world. The only lossless codec is the huffy codec but its only usefulness is during actual capture to disk. No hardware has been developed other than computers that could take advantage of this.
Moral of the story: You are going to lose quality by converting no matter what. If done very well, this quality loss can be kept to minimal where it is...