mp3,   mp3 files are compressed to roughly one-tenth the size of an equivalent     PCM file while maintaining good audio quality.

mp4,  A proprietary version of AAC in MP4 with Digital Rights Management developed by Apple for use in music downloaded from their iTunes Music Store.               

midi    An industry-standard protocol that enables electronic musical instruments, computers, and other equipment to communicate, control, and synchronize with     each other.

wave  Standard audio file container format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD-quality sound files, which means that       they can be large in size — around 10 MB per minute. Wave files can also contain data encoded with a variety of codecs to reduce the file size (for example the GSM or mp3 codecs). Wav files use a RIFF structure.

mpeg  Musepack or MPC (formerly known as MPEGplus, MPEG+ or MP+) is an opensource lossy audio codec, specifically optimized for transparent compression   of stereo audio at bitrates of 160–180 kbit/s. Musepack and Ogg Vorbis are rated    as the two best available codecs for high-quality lossy audio compression in many double-blind listening tests. Nevertheless, Musepack is even less popular than Ogg Vorbis and nowadays is used mainly by the audiophiles.