Merging AAC audio files?

[killerteengohan]

I have 2 separate AAC-LC .MP4 audio files I want to merge.

Everytime I use the append feature in MKVmerge it throws the audio out of sync where it got appended at. If I had a 30 second audio clip and 21 minute audio clip and appen the 21 minute to the 30 second audio, it plays perfectly for the first 30 seconds then the audio goes out of sync the more and more the video goes along after the append.

Can anyone suggest a good program for merging/combining AAC-LC .MP4 files so that I can mux it in MKVmerge without this audio issue the Append is always giving me?

[Selur]

a. I assume your aac-lc files have the same channel mapping and sample rate, otherwise you can't join them unless you reencode one of the files.
b. What error does mkvmerge message does mkvmerge show?
c. 'MP4Box -cat file1.mp4 -cat file2.mp4 output.mp4' would be a typical call to append mp4 files. (my guess it that most mp4box guis should offer this option)

[El Heggunte]

Assuming you're not uncomfortable with the command-line interface, try the following:

1) demux the audio streams to AAC files through ffmpeg;

2) concatenate with "copy /b part_1.aac + part_2.aac full_audio.aac"

[poisondeathray]

Another option is MP3DirectCut, which supports AAC

But if you are appending audio, and then merging with video, your description implies you have problems with your video as well (perhaps VFR, frame rate issues)