Is there a way to record internal audio? I have Amazon Kindle (I don't have a USB cable, so I can't root the Kindle). I also have online lectures. For some reasons, my Kindle can stream faster than on my PC.

Now, I want to record the audio from online lectures directly from my Kindle so that I can listen to it while offline.

Most of the Android applications I've found record phone calls, which is not what I want to do.
If you have a Samsung or LG phone, Mobizen Screen Recorder can capture internal audio.  I've tested on a Samsung but not LG.