Convert FLAC to MP3

How much room the MP3 copies save

CD-quality FLAC takes about 5 to 7 MB a minute, so a 45-minute album is roughly 250 to 300 MB. The same album as MP3:

Hi-res FLAC (24-bit, 96 or 192 kHz) is several times bigger again, yet its MP3s come out the same size as any others. MP3 stops at 48 kHz, so Octoolo writes those tracks at 48 kHz.

Keep the FLACs as your master library. The MP3s are copies for the road, and you can make new ones from the FLACs whenever you need them.

Covers, tags and surround

Octoolo copies the title, artist, album and the other tags into each MP3, plus the cover picture embedded in the FLAC, JPEG or PNG. They are written as ID3v2.3, the tag version car stereos and older players read most reliably, so those show the right names and artwork instead of “Track 01”.

A cover kept only as a separate “cover.jpg” or “folder.jpg” file beside the tracks is not put into the MP3s. If you save the MP3s next to the originals, that picture is still in the same folder, and some players pick it up from there. Players that only read embedded art will show a blank square for those albums, so embed the cover in the FLACs first if that bothers you.

Surround FLACs (5.1 and the like) are mixed down to stereo, since an MP3 carries two channels at most. Nothing else needs setting: the usual 44.1 and 48 kHz tracks keep their sample rate.

Is 320 kbps overkill?

Not if you have the space. At 320 kbps an MP3 keeps as much of the FLAC as the format can, and on earbuds or in a car it is very hard to tell apart, while still taking only a third to a half of the FLAC's room. 192 kbps is the sensible middle when storage is tight; 128 kbps is better saved for speech. For something in between, More settings offers 256 and 160 kbps too.

What to avoid is converting those MP3s again later, for example to AAC for another device. Each lossy step drops a little more, so go back to the FLAC for every new copy. If the copy is for Apple's apps, FLAC to ALAC keeps everything; for an editor or an audio CD, use FLAC to WAV.

Converting a whole library

A big library is easiest in parts. Each folder you add brings in up to 500 tracks, so dropping one artist or a shelf of albums at a time works well, and you can add the next part with Add more while the first is still converting.

Octoolo works on four tracks at once. Every row has a progress bar, a speed readout and a countdown, and rows that haven't started say Waiting its turn. When everything is done, the summary counts the converted files and shows how much smaller they are in total. If one track fails, say because the file is damaged, its row explains why and the rest carry on. Stop all ends the batch early; MP3s already finished stay where they are.