I've just been trying to set up FFmpeg here (well, got the guys at ServInt to do it infact), but running FFmpeg gave me this error:

ffmpeg: error while loading shared libraries: libavformat.so.51: cannot open shared object file: No such file or directory

My linux knowledge is coming up short here, so I dug around for a solution:

Edit /etc/ld.so.conf and add the line /usr/local/lib then save and exit.

Now run this command: ldconfig -v

I'm just documenting this here to help others and help me when I have to do this again on the live server after Xmas.

huh whaddayaknow. Same problem came up again on another server. This thread turns up in Google. Problem solved once again.

Hurrah for 12S!