1) Download the nacl_sdk. (https://developer.chrome.com/native-client/devguide/tutorial/tutorial-part1)
2) cd nacl_sdk; ./naclsdk //will show all the possible commands
3) ./naclsdk update will install/update the nacl_sdk.
4) ls will show that you have installed folders. You will find pepper_xx where xx denotes the version of pepper installed.
5) cd getting_started; make serve; will start the httpd server on loalhost:5103. Then you can see the live demo of nacl yourself. I wont go into details .nmf file which directs wheather to fetch pnacl or .nexe binary. These binary are created using nacl snadboxing and not normal binaries(elf or exe).
You can also try cd pepper_xx/examples; make serve. This will also start the server at 5103 and you can try and debug the demo
Now to install ffmpeg nacl port, we need to install depot_tools first.
6) Follow installation instructions for depot_tools from http://dev.chromium.org/developers/how-tos/install-depot-tools
7) Make sure that till this point your ~/.bashrc has these two changes:
export PATH=”$PATH”:/home/user/depot_tools
export NACL_SDK_ROOT=/home/user/nacl_sdk/pepper_xx
8) Now to install naclports follow instructions given at http://code.google.com/p/naclports/wiki/HowTo_Checkout.
(I just used git clone instead gclient config…But thats not important)
9) Its very important to read README.rst once before starting compilation of naclports.
For my case I used, NACL_ARCH=pnacl make ffmpeg.
This will download and compile ffmpeg which has been. The version of ffmpeg compiled can be looked upon at http://code.google.com/p/naclports/wiki/PortList.
References:
https://developer.chrome.com/native-client
Practical Stuff 