missing ffmpeg (Ubuntu 12.04)

You can use libav as substitution. If I remember correct, you need the packages

libavcodec-dev
libavdevice-dev
libavfilter-dev
libavformat-dev
libavifile-0.7-dev (not sure about this)
libavutil-dev

I don’t know if you have special needs, maybe here is a proper build for you: Panda3D downloads for several distros