The M4R is an iPhone ringtone file that is essentially a renamed AAC (m4a) file. Not all iTunes Music Store songs can be used to create M4R ringtones. In order to create an M4R ring tone from an iTunes song, the song must allow for M4R ringtone creation. An M4R ring tone is automatically transferred to a user's iPhone when the iPhone is synced with the user's computer.
M4R is essentially a renamed AAC (M4A) file - it is similar to MP3 but compresses the digital audio files further. It is part of the MPEG-4 standard and is specified in the ISO/IEC standard 14496-3. It is a lossy algorithm much like AAC and MP3. M4R supports auditory masking - essentially discarding data with minimal loss of quality.
Free Lossless Audio Codec, or FLAC for short, is an audio compression technique. It is a lossless compression type meaning that the compression takes place without data being discarded. FLAC is an open source codec. FLAC is a format that is recommended to those backing up a CD collection because the sound quality will remain high, whereas MP3 compression will result in a deterioration compared to the original.
Using FLAC to compress an audio file to approximately 50% of its original size. The main benefits of a FLAC file in addition to it being lossless is that it can be used for streaming, and decoding is fast, allowing for real time decoding to take place. A FLAC file also contains several data integrity checks in the header file. The metadata associated with the audio has been future proofed also to allow new fields to be defined without impacting existing decoders.