how to append two audio w/o re-encode based on an identical point?

[lansing]

I captured a live stream from youtube using ffmpeg. Later I found out that the audio was cut off midway through the event, so I recaptured the stream the second time started a little bit before the point where the audio went out. And now how do I append the two audios without re encoding? I wanted to append them base on a point where they both shared, and that point is exactly identical in both audios. Is there any software that can do this?

The audios were aac.