Free Lossless Audio Codec (FLAC) is an audio codec that allows digital audio is compressed lossless so that the audio file size is reduced without any loss of information. Compressed digital audio FLAC algorithm typically can be reduced 50 to 60% of its original size, and decompressed in an identical copy of the original audio data. The downside is that the file takes up much more space than would be obtained by applying a lossy compression algorithm. FLAC is an open format with royalty-free license and a reference implementation which is free software. FLAC has support for tagging metadata, including album art, and quick search.
The M4R file type is primarily associated with 'iPhone' by Apple Inc.. This is basically a renamed AAC (M4A) file.