http://libmpeg2.sourceforge.net/files/mpeg2dec-0.4.0.tar.gz

tar zxf mpeg2dec-0.4.0.tar.gz
cd mpeg2dec-0.4.0
zcat mpeg2dec.diff.gz | patch -p0
LDFLAGS="-elf2flt" ./configure --host=nios2-linux-uclibc --disable-sdl --disable-accel-detect --disable-shared --prefix=/opt/nios2
make clean
FLTFLAGS="-s 8192" make

sudo make install

The libs will be installed to /opt/nios2/lib, headers in /opt/nios2/include, and executables (*mpeg2*) in /opt/nios2/bin .
You should copy the executables to your rootfs, eg, ~/uClinux-dist-test/romfs/bin .

(how to enable sudo : enable wheel group in sudoers and add yourself to group wheel, so that you can use sudo command to install the tools.
as root, run visudo,

# Uncomment to allow people in group wheel to run all commands
%wheel ALL=(ALL) ALL

save file with ESC :wq

Edit /etc/group, and add yourself to wheel group
wheel:x:10:root,hippo

)