I found the answer from the creator of mp3DirectCut. He gives three options. Relevant part of his post follows:
I use the "DSM converter" of an old version of the "Media Player Classic" (1.3.1249.0). Also "FFmpeg" can demux (command line: ffmpeg.exe -i inputfile.mp4 -acodec copy outputfile.aac
).
There is also MP4Creator which is much smaller. This small batch file can be used for easy decoding by dropping files on it:
mp4creator demux.bat:
@echo off mp4creator.exe -list %1 echo Demux which track (usually 1 or 2)? set /p track= mp4creator.exe -extract=%track% %1 pause
The extension output file must be renamed to AAC - and you got it.
I went with ffmpeg. To convert back to AAC it appears that an additional option is needed. The commands for converting to and from AAC are like below:
ffmpeg -i in.m4a -acodec copy out.aac ffmpeg -i in.aac -acodec copy -bsf:a aac_adtstoasc out.m4a