problem with megui to convert multi channel ac3 to aac mp4

[pourya2007]

hi
in megui i want to encode a multichannel ac3 audio file to aac mp4 and ac3 audio file size is 158mb but when i convert it to aac mp4 with megui with neroaac the file size is 2mb and it has only the first part of audio
if somebody know
plzzz help me