How to mux .ac-3 to .mp4 (audio)

[kalemvar1]

I'm trying to extract the audio from a video (mp4). I used mp4box to do so and it gave me a .ac-3 extension file, not the best format to edit. I would love to convert to it .mp4 (without re-encoding)

I wonder if there's a simple way to do this ?

Thanks

[ProWo]

mp4 is a container, not a codec.

[butterw]

the standard audio codec used in mp4 container is aac. It's a different codec from ac3 so it will require re-encoding.