Hello people, please help me.

I was using Sound Forge to edit the audio from my caputre (AVI format), then I convert to VCD/MPEG-1 with LSX MPEG Encoder. But it's hard to edit AVI files because of its size. Always many GBs. Is there any program which edits audio in a MPEG video? The only function I use is copy and paste (to copy from the new audio (wav file), then sync with the mpeg file).