CD music is not 128 kbps. When audio is extracted into wav/aiff as uncompressed it is 1411 kbps 44 Hz. That's a big difference from 128. It's 1/11th of the bitrate. And before it's been made into a CD, I'm sure it will be much higher. Probably 32 or higher (96) sample rate, etc.

DVD ac3 audio is either 48 or 96 Hz sample rate, & bit-rate anywhere up to 448 kbps for stereo. My A.Pack AC3 encoder only goes down as far as 56 kbps but I wouldn't use less than 192 kbps.