As long as you can hear the sound, either from your speakers or your
headphones, and you set your screen-recording software to record
from where you're hearing the sound, you should get sound recorded
with your video. But, all recording software is different. Some give you
more options than others for recording sound. Your best bet is to just
play around with whichever one you use until you get the results you're
looking for.
TMR, as for the stereo mix setting, it sounds like you might be talking
about a Windows setting, instead of a recording software setting, but
I could be wrong about that. Let me know, if you would, please.
Having said all that, it's my understanding, and @nath75 can correct
me if I'm wrong, but Nath is not recording these videos himself. He
gets them from other sites and posts them here for our viewing
pleasure. So, he has no control over the audio. We get what he gets.
Nath, please tell me if I'm wrong about that. Thanks.