Master's thesis main goal is MPEG-4 audio encoder software implementation. However, the thesis also aims to give an overall introduction to perceptual audio encoding, with an emphasis on MPEG-4 standard. The thesis consists of ten chapters, generally divided into three groups. First group gives overall introduction to audio coding, second group describes MPEG-4 audio standard, and the third group describes actual audio encoder implementation. Chapter 1 gives a short introduction to multimedia technologies, with an emphasis on audio coding. Chapter 2 briefly describes human auditory system and serves as an introduction to Chapter 3, which describes psychoacoustic principles that, in fact, represent fundamentals of audio coding itself. After explaining the basic psychoacoustic principles, Chapter 4 describes a typical audio encoder architecture that is followed by nearly all audio encoders now days. Same chapter gives a concise description of historical audio encoder development. Chapter 5 gives overall introduction to the most sophisticated multimedia standard today – ISO 14496 (MPEG-4). Chapter 6 starts the description of the concrete software implementation of the audio encoder according to MPEG-4 General Audio – a part of MPEG-4 standard that relates to high bandwidth, complex audio signal encoding. Audio encoder is called RAAC according to RASIP Advanced Audio Coding. Chapter 7 describes psychoacoustic model implemented in RAAC encoder, while Chapter 8 describes main MPEG-4 audio blocks also implemented in RAAC encoder. Chapter 9 is devoted to subjective and objective analysis and evaluation of RAAC implementation, while Chapter 10 gives the overall conclusion.