FLAC stands for Free Lossless Audio Codec, an audio format similar to MP3, but lossless, meaning that audio is compressed in FLAC without any loss in quality.
The basic structure of a FLAC stream is: •The four byte string "fLaC"
•The STREAMINFO metadata block
•Zero or more other metadata blocks
•One or more audio frames
The first four bytes are to identify the FLAC stream. The metadata that follows contains all the information about the stream except for the audio data itself. After the metadata comes the encoded audio data.