[FFmpeg-user] Is this the best method to keep audio quality when converting lossy audio to another lossy audio?

[Farhad Mohammadi Majd]

Hello, I have a large collection of audio files contains music in mp3
format, due to need to free space of hard disk, I need to reduce their
size.

It seems opus is the best format for this purpose, in order to have the
quality of original mp3 files, currently I use ffmpeg command to
convert them to FLAC and then use opusenc, the official opus encoder,
to convert FLAC files to opus.

By using one standard and good quality headphone, My ears don't notice
any difference between original mp3 files versus new opus files.

1. Is this the best method to keep audio quality when converting lossy
audio to another lossy audio?

2. Is there any quailty loss in this method? if yes, is it noticeable?
how much is it?

THANKS FOR HELP