The developer team has decided do not make any release, they only provide SVN snapshots.
(September 8, 2008) FFmpeg is undergoing major changes in its API/ABI. The last valid revision for libavcodec version 51 is r15261.
svn --revision 15261 checkout svn://svn.mplayerhq.hu/ffmpeg/trunk ffmpeg &&
cd ffmpeg &&
./configure --prefix=/usr \
--enable-shared \
--enable-pthreads \
--disable-ffplay \
--enable-gpl \
--enable-postproc &&
make
make install