Steinway & Sons has been in business since 1853, making pianos. With a century and a half of experience, Steinway has developed a mature process for creating pianos, and it's a lot of work. Here's a nice little video explaining all the steps that go into it—and the first one takes up to one year. Enjoy:
Why the crackly audio? Here's the explanation from Open Culture:
Several decades ago, John H. Steinway (the great-grandson of Henry E. Steinway) narrated an audio tour of the New York factory, where he described the generations-old process of making a Steinway grand piano. In 2011 Ben Niles, the producer behind the documentary film Note by Note, synced the audio tour with present-day footage of the Steinway factory....
See also: Leonardo da Vinci's Piano/Cello Hybrid and Glenn Gould Playing the Goldberg Variations (Video). (Gould famously loved his Steinway CD 318.)