If you get this error message:

checking for ffmpeg headers... configure: error: ffmpeg headers not found. Make sure you've built ffmpeg as shared libs using the --enable-shared option

Do the following:
- DirectAdmin Control Panel

cp -a /usr/local/include/libavcodec/* /usr/local/include/ffmpeg
cp -a /usr/local/include/libavdevice/* /usr/local/include/ffmpeg
cp -a /usr/local/include/libavformat/* /usr/local/include/ffmpeg
cp -a /usr/local/include/libavutil/* /usr/local/include/ffmpeg

- cPanel/WHM Control Panel

cp -a /usr/local/include/libavcodec/* /usr/local/src/ffmpeg
cp -a /usr/local/include/libavdevice/* /usr/local/src/ffmpeg
cp -a /usr/local/include/libavformat/* /usr/local/src/ffmpeg
cp -a /usr/local/include/libavutil/* /usr/local/src/ffmpeg

Then re-compile FFmpeg.