Convert OGG to FLAC
Drop an .ogg file and download a FLAC holding the decoded audio. Sample rate and channel count are preserved.
The reason to run this conversion is a format requirement rather than a quality gain: a mastering step, a DJ library, or an archive policy that rejects lossy files.
Losses stop here
FLAC compression is reversible, so the audio you put in is the audio you get back. Editing the FLAC and exporting it repeatedly adds nothing, which is the opposite of working directly on an Ogg where each save re-encodes.
What FLAC cannot do is reconstruct frequencies Opus or Vorbis deleted.
Size
A low-bitrate Ogg can grow by a factor of ten or more. A 5 MB, 10-minute voice file may land near 60 MB as FLAC, since the decoded PCM is what gets compressed rather than the Ogg itself.