Netflix: streaming to every screen
On 15 November 2024, a single boxing match on Netflix reached 65 million streams at the same moment. In 2025 Netflix said its own delivery network has more than 18,000 servers in over 6,000 locations. This lesson shows the main trick behind that: a small "brain" in the cloud decides, and a huge, simple network of boxes inside internet providers carries the video. Then you build the same ladder of video qualities with ffmpeg.
By the end you can
- Explain the split between Netflix's control plane on AWS and its data plane on Open Connect
- Trace what happens between pressing play and the first frame
- Explain an encoding ladder, per-title encoding and adaptive bitrate in plain words
- Describe Netflix's data layer: Cassandra, EVCache and the key-value layer on top
- Encode a 3-rung HLS ladder with ffmpeg and write a player rule that avoids the spinner
The everyday picture
Picture Mangrove Market on the night before a festival. Head office does the thinking: it knows which items will sell in which area, what each store already has in its back room, and which stores are short. But head office never hands a bag of rice to a customer. The trucks leave the distribution centre (DC) at night, when the roads are empty, and fill each store's back room with what that area will buy tomorrow. In the morning, a customer walks to the nearest store and takes the rice from the shelf. If that store has run out, the staff send her to the next nearest one.
Netflix works the same way. A small set of services in the cloud is head office: it checks your account, picks what to play, and tells your TV which nearby server to use. The heavy goods, the video itself, sit in boxes that Netflix places inside your internet provider, filled at night. When you press play, almost nothing heavy travels far. Keep this picture in mind: thinking in the middle, heavy bytes at the edge, filled ahead of time.
What the product must do
- Functional. Sign in on any device (TV, phone, laptop, game console), browse a personalised home page, press play, resume where you stopped, download for offline viewing, and watch live events.
- Non-functional. Video must start in a few seconds and never stop to load. Picture quality should be as good as the connection allows, on a fast home line or a weak mobile signal. The service must survive the failure of a whole cloud region. Cost per hour watched must keep falling, because traffic grows every year.
The hard one is the second. A search that takes 2 seconds is annoying; a film that freezes every 2 minutes is unwatchable. Most famous Netflix decisions serve "start fast, never stall".