MPEG 第二級音訊編碼系統之壓縮, 優化及品質評估研究

Abstract

The Layer 2 compression scheme of MPEG audio Coding is a very commonaudio coding standard for Cd quality audio (music). However, its encodingprocess requires a large amount of computation. In this thesis, we propose someoptimization techniques to make the encoding program much faster while allowingto impair the audio quality a little. In order to measure how much quality loss,we define criteria to say that the encoder encoding streams with a quality lossrate equivalently wastes a number of bits, if the encoder that completelyconforms to the layer 2 standard can save the same number of bits while keepingthe same quality loss rate. In our experiments, we optimize the layer 2compression programs such that audio streams can be encoded real time onPentium Pro 180 machine with only 0.0003% quality loss and 1.5% bits wasted,and on Pentium 180 machine with only 0.0009% quality loss and 4% bits wasted. In this thesis, we will also propose some methods to reduce the bitrateof layer 2 compression scheme without impairing the original audio quality orjust impairing a little. Base on these methods, we can reduce bitrate from256 kbps to 160 kbps that is close to layer3's 128 kbps. At last, we will introduce a real-time multimedia system by applyingthe layer 2 compression program optimized by us.