travis: use homebrew to build ffmpeg on OS X

This allows us to use a newer version of ffmpeg and to test the build of our
VDA code.

travis-deps

@@ -2,26 +2,57 @@
 
 class TravisDepsBuilder
   def self.make(name)
-    info = build_map[name]
-    raise "unrecognized dependency identifier '#{name}'" unless info
-    instance = new(name, info[:url], info[:action])
+    instance = klass.new(name)
+    instance.fill_data
     instance.deps
     instance.build
   end
 
-  attr_reader :name, :url, :action
+  def self.klass
+    Module.const_get([self.name, self.os.capitalize].join)
+  rescue NameError
+    self
+  end
 
-  def initialize(name, url=nil, action=nil)
-    @name, @url, @action = name, url, action
+  def self.os
+    ENV['TRAVIS_OS_NAME']
+  end
+
+  attr_reader :name, :url, :action, :os
+
+  def initialize(name)
+    @name, @os = name, self.class.os
+  end
+
+  def fill_data
+    data = build_map.fetch(name)
+    @url, @action = data[:url], data[:action]
   end
 
   def build
-    send(@action)
+    send(action)
   end
 
   def deps; end
 
   private
+  def package_manager_update
+    # yes class variable, you wanna update only once across all instances
+    @@updated ||= false
+    return if @@updated
+    sh({'linux' => 'sudo apt-get update -y', 'osx' => 'brew update'}[os])
+    @@updated = true
+  end
+
+  def package_install(*packages)
+    cmd = {
+      'linux' => 'sudo apt-get install %s -y',
+      'osx'   => 'brew install %s'
+    }[os] % [packages.join(" ")]
+
+    sh cmd
+  end
+
   def git
     sh "git clone --depth=1 #{url} #{name}"
     compile name
@@ -35,6 +66,10 @@ class TravisDepsBuilder
     compile dirname
   end
 
+  def package
+    package_install(url)
+  end
+
   def compile(dirname)
     sh "cd #{dirname} && #{configure} && make && sudo make install"
     sh "cd $TRAVIS_BUILD_DIR"
@@ -50,7 +85,7 @@ class TravisDepsBuilder
 end
 
 class Libav < TravisDepsBuilder
-  def self.build_map
+  def build_map
     {
       "libav-stable" => {
         :action => :stable,
@@ -76,8 +111,16 @@ class Libav < TravisDepsBuilder
   end
 end
 
+class LibavOsx < Libav
+  def build_map
+    {
+      "ffmpeg-stable" => { :action => :package, :url => 'ffmpeg' },
+    }
+  end
+end
+
 class Libass < TravisDepsBuilder
-  def self.build_map
+  def build_map
     {
       "libass-stable" => {
         :action => :stable,
@@ -89,15 +132,12 @@ end
 
 class Dependencies < TravisDepsBuilder
   def deps
-    case ENV['TRAVIS_OS_NAME']
-    when 'linux' then
-      sh "sudo apt-get update -y"
-      sh "sudo apt-get install pkg-config fontconfig libfribidi-dev yasm -y"
-    when 'osx' then
-      sh 'brew install pkg-config fontconfig freetype fribidi yasm'
-    else
-      abort "Unrecognized OS"
-    end
+    packages = {
+      'linux' => 'pkg-config fontconfig libfribidi-dev yasm',
+      'osx'   => 'pkg-config fontconfig freetype fribidi yasm'
+    }
+    package_manager_update
+    package_install(packages.fetch(os))
   end
 end