MP3 is an audio-specific format that was designed by the Moving Picture Experts Group (MPEG) as part of its MPEG-1 standard and later extended in MPEG-2 standard.

FLAC means Free Lossless Audio Codec, is a kind of lossless and oversimplified MP3. It was designed specifically for audio, which means that you can play back compressed FLAC files in your favorite player just like you would an MP3 file.

1: In terms of Quality / Size, Mp3 is better (192 kbps is enough).
2: FLAC is good when you want to make a back up of your precious audio CDS but do not want to sacrifice the audio quality. 192 kbps is good enough for human ear, but for precision audio, you might wanna go for 320.
3: FLAC to MP3 for Mac converter can help you convert FLAC to MP3 on Mac with ease.

Other Comparison: MP4 vs FLV / MKV vs MP4 / MP4 vs MP3 / 3GP vs MOV / 3GP vs FLV / M2TS vs MP4 / MP4 vs 3GP / SWF vs 3GP

Related Post of FLAC File formats

Related Post of MP3 File formats