android jni wrapper,Android ffmpeg simple JNI wrapper

I've been trying to use an ffmpeg binary with command line access for a while now and getting nowhere (Using runtime.exec)

It looks like the only way I'll be able to get it to work is using a wrapper in C to access the built ffmpeg libraries using JNI...

Main problem: I haven't coded C for more than one and a half decades now and wouldn't know where to begin...

I just need 3 operations, I need to add audio to a video file, I need to concatenate two video files and if possible I need to rotate a clip by 90 degrees (but I could do without this)...

Does anyone have any example code that could work for me, or some good places to start (I've already exhausted much of the first pages of various google results to no avail)...

Any help would be greatly appreciated!