Add facade pattern.

[ilopX]

Facade pattern

Facade is a structural design pattern that provides a simplified interface to a library, a
framework, or any other complex set of classes.

Tutorial: here.

About example.

This the very conceptual example rewrite from original source code java example

Diagram:

Client code:

void main() {
  final converter = VideoConversionFacade();
  final mp4Video = converter.convertVideo("youtubevideo.ogg", "mp4");
  // ...;
}

Output:

VideoConversionFacade: conversion started.
CodecFactory: extracting ogg audio...
BitrateReader: reading file...
BitrateReader: writing file...
AudioMixer: fixing audio...
VideoConversionFacade: conversion completed.