[FFmpeg-user] Copying Audio

[Chris]

I have a file with audio in the format pcm_s16be. When I try to copy this audio to another file using -c:a copy, it copies the audio but also transcodes it to AAC. If it's literally a copy, shouldn't the copy be pcm_s16be as well? How can I do this and wind up with a pcm copy of the original audio? I've tried -c:a pcm_s16be and it fails.
The complete command is:
"ffmpeg.exe","-y  -i short.mp4 -i short.mp4 -c:a pcm_s16be  married.mp4"
I am overwriting the audio on short.mp4 and it works well except for the transcoding to AAC.