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AV1 Bitstream & Decoding Process Specification

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This document provides instructions for working with the draft AV1 Bitstream & Decoding Process Specification.

The specification document is built from plaintext section and subsection Markdown files (more specifically, kramdown files) using the Jekyll static site generator tool.

The document build process employs a common NodeJS-based web development toolchain, requiring Node, npm, and GruntJS, a Node-based task runner.

Note: As a general rule, the packages described below should be installed in user space, not at the system level -- in other words, do not install them as root or via

. An exception is Ruby development headers, which are usually needed to build Ruby and certain Ruby gems. {:.alert .alert-info }

Ruby and rbenv

This project currently depends on Ruby v2.4.1. Because your distro may lack this version -- or installing it may conflict with your system's installed version -- first install rbenv, then install Ruby v2.4.1 within it.

# list all available versions:
$ rbenv install -l

install a Ruby version:

$ rbenv install 2.4.1

Depending on your distro and environment, you may have trouble building a particular Ruby version. The rbenv project site maintains a wiki page with troubleshooting help.


Gem dependencies are managed with bundler.

$ gem install bundler

Filesystem location where gems are installed

$ gem env home

=> ~/.rbenv/versions//lib/ruby/gems/...

Clone the Repo

git clone [email protected]:AOMediaCodec/av1-spec.git
cd av1-spec

Set Local Ruby Version (rbenv)

In the directory of your local clone, do:

rbenv local 2.4.1

Regardless of any other Rubies installed on your system, the project environment will now use v2.4.1 and gems appropriate for it.

Install Gem Dependencies with Bundler

In the directory of your local clone, run

bundle install

Bundler will set dependencies and install needed gems as listed in


NodeJS, npm and GruntJS

Follow these instructions for installing NodeJS and npm.

Next -- from the project directory -- update npm, install the grunt package, and install the project's Node dependencies:

## Update npm globally
npm update -g npm

Install grunt globally

npm install -g grunt-cli

Go the the project directory

cd av1-spec

Install the project's Node dependencies

(uses package.json and Gruntfile)

npm install

Grunt Tasks

Building the document is done via Grunt tasks, configured in the CoffeeScript file

There are tasks to

  • clean output directories
  • perform some automated text transformations on the content files
  • build the document with Jekyll
  • copy output files to the correct directories for serving and viewing

These tasks are invoked in turn by the Grunt default task:

$ grunt

There is also a task that starts a local web server, and launches the document in your web browser:

$ grunt connect:local

The document will be viewable at

If you'd rather not launch a browser window, use:

$ grunt connect:nospawn


Additionally, there is a task

grunt exec
for generating the spec as a PDF file. It invokes the commercial tool Prince, which must first be installed on your system. PDF generation can then be done with:
$ grunt && grunt exec

Note that while we are generating PDF as a convenience format during document development, the canonical spec will likely be served as HTML, not PDF. {:.alert .alert-info }

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