The mpg isn't compressed. A mpg is converted to mpeg-2 compliant to your TV system (NTSC or PAL) using an encoder and inserting it the TV system's specifications and such a bitrate (MPEG-2 are VBR , that is Variable Bit Rate) such video+audio = 4489 MB. Audio is, usually, a 48 kHz 192 up to 448 kbps file (MP2 or AC3, 1+1 or 5+1 channels).