[linux-audio-user] scriptable audio editor to (parallel) combine streams

[Nicolai Lissner]

You might have a look at sox (which also comes with soxmix) - I'm not sure
if it is actually able to mix two sources to different channels, but since
you asked for a scriptable audio editor, sox has been the first thing that
came in my mind, as it is scriptable as in shell script. 
Many people think of sox as just a tool to convert from one
audio format to another, but actually sox can do *much* more and is probably
the best choice when it comes to things that should be done more or less often.