Eιναι MPEG-4 Part 14 συμπιεσης, χωρις εικονα βεβαια και θεωρειται οτι στα ιδια Kbps ειναι λιγο καλυτερο απο mp3.
Data streams
Almost any kind of data can be embedded in MPEG-4 Part 14 files through private streams; the widely-supported codecs and additional data streams are:
Video: MPEG-4 Part 10 (also known as H.264 and MPEG-4 AVC), MPEG-4 Part 2, MPEG-2, and MPEG-1.
Audio: AAC (also known as MPEG-2 Part 7), MP3 (also known as MPEG-1 Audio Layer 3), MPEG-4 Part 3, MP2 (also known as MPEG-1 Audio Layer 2), MPEG-1 Audio Layer 1, CELP (speech), TwinVQ (very low bitrates), SAOL (MIDI).
Subtitles: MPEG-4 Timed Text (also known as 3GPP Timed Text).
Some private stream examples include Nero's use of DVD subtitles (Vobsub) in MP4 files.