Why you should never convert lossy to lossless ?
When you convert a file from a lossless format to a lossy format – say, ripping an audio CD (a lossless format) to MP3 files (a lossy format) – you’re throwing away some of the data. The MP3 file is so much smaller because much of the original audio data has been lost.
If you converted the lossy MP3 file to a lossless FLAC file, you wouldn’t get any of that data back. You’d get a much larger FLAC file that’s only as good as the MP3 file you converted from. You can never get the lost data back. Think of it like taking a perfect copy of a photocopy – even if it was possible to create a perfect copy of a photocopy, you would still end up with a photocopy, which isn’t as good as the original document.
This is also why it’s a bad idea to convert lossy formats to other lossy formats. If you take an MP3 file (a lossy format) and convert it to OGG (another lossy format), more of the data will be thrown away. Think of this like taking a photocopy of a photocopy – each time you photocopy a photocopy, you lose data and the quality becomes worse.
Conversion from lossless formats to lossy formats works well, however. For example, if you rip an audio CD (lossless) to FLAC files (lossless), you’ll end up with files as good as the original audio CD. If you later converted those FLAC files to MP3 files – say, to shrink them down so more of them will fit on an MP3 player – you’ll end up with MP3 files that are as good as MP3 files ripped from an audio CD directly.