In order to quickly compile your [http://www.videolan.org/developers/x264.html libx264], you can type the following commands in your shell:
{{{
$ cd /my/path/where/i/keep/compiled/stuff
$ git clone git://git.videolan.org/x264.git
$ cd x264
$ ./configure --enable-static --enable-shared
$ make
# make install
# ldconfig
}}}

Note: `$` generally indicates that the command can be run as a normal user. `#` indicates that superuser privileges are generally required. If you are using Ubuntu, you'll most probably have to use `sudo` for commands preceded by `#`, such as:
{{{
$ sudo make install
$ sudo ldconfig
}}}

If you get a message like this:
{{{
Found yasm 0.x.x.xxxx
Minimum version is yasm-1.0.0
If you really want to compile without asm, configure with --disable-asm.
}}}
that means that you have an old version of yasm on your system, so you should update it. The quickest way to do so is like this:

{{{
$ wget http://www.tortall.net/projects/yasm/releases/yasm-1.2.0.tar.gz
$ tar xf yasm-1.2.0.tar.gz
$ cd yasm-1.2.0
$ ./configure
$ make
# make install
}}}
and after that, just repeat the `configure`, `make`, and `make install` steps for libx264 and it should be fine this time.