I want to use FFmpeg with Android-NDK and I am very basic in this section, I need some help and I research about this topic before on the net, but
I made a tutorial on how to build ffmpeg and x264 for android:
http://db.tt/TjMqIF3u
You can also download the zip file containing the files you need to make an application on android and also an executable of lastest ffmpeg to run on android.
EDIT: This is really old code and old compilation process. You can find a more up to date process on FFMPEG docs