PSA: Looks like Amazon is not updating the source anymore. So stay on the old version or have nothing.
Looking for a video player I recommend https://github.com/mpv-android/mpv-android/releases




To build all ffmpeg libraries, change working directory to ffmpeg/JNI, edit ENV with your NDK location then run rebuild-ffmpeg.sh. 
To build an individual ffmpeg library, change directory to ffmpeg/JNI, edit ENV with your NDK location then run build-ffmpeg.sh {architecture name}.
Visit https://sites.google.com/site/mxvpen/ffmpeg for more information