MP3's are lossy compressed files and the data is lost. There would be no advantage converting them to FLAC. In fact, converting a compressed MP3 into a FLAC or Apple Lossless file will result in a much larger file size.
Steve hit the nail on the head.
When a MP3 is made, various parts of the music are literally thrown away on the basis that our hearing is less sensitive to the missing parts. Once thrown away they cannot be recovered. It is a bit like trying to unscramble an egg.
However, the MP3 process allows a file to be compressed to perhaps only 10% of the original uncompressed WAV size. .
A FLAC file is compressed, but still contains all of the music from the original. However, with FLAC, file size reduction is nowhere near as dramatic as a MP3. FLACS are generally half or more the size of the original WAV
Think of a data file that has been "zipped". No data is missing but the file is smaller in terms of byte size.
So converting a MP3 to FLAC accomplishes nothing; it just wastes space.
