Originally Posted By: JayO
In the past I have used this : http://audioslicer.sourceforge.net


Thanks, Jay. I will look into that. For now, I'm going with FFmpeg, it lets you do this with fairly straightforward line commands, like this to grab 120 seconds at an offset of 360 seconds:

ffmpeg -i big-input-file.m4a -ss 360 -t 120 -acodec copy small-output-file.mp4

https://www.ffmpeg.org