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Design Netflix (Video Streaming) for New Grad Software Engineer

The problem for a New Grad Software Engineer

Functional: browse a catalog, play a video with seek/resume across devices and bitrates, support profiles and watch history.
Non-functional: low startup latency (<2s), minimal buffering/rebuffering, global availability, an enormous read-heavy workload.
Scale: ~200M subscribers, ~100K titles, petabytes streamed per day, tens of millions of concurrent viewers at peak.
Consistency: watch history/resume points can be eventually consistent; playback must never stall on a metadata outage.

Out of scope (covered in detail below)

Billing, recommendations ML training, the studio/production side, downloads/offline, live streaming, and DRM — deferred and discussed in the dedicated section.

As a New Grad Software Engineer, the system design round will probe fundamentals, potential, and learning agility. Be prepared to go deep on the areas a New Grad Software Engineer owns and to articulate trade-offs clearly.

Capacity estimation

Resource	Estimate	Notes
Storage (catalog)	~petabytes	Many encodings per title (240p -> 4K)
Egress bandwidth	terabits/s at peak	Dominates cost; CDN is the lever
Concurrent viewers	tens of millions	Concentrated in evening hours per region
Catalog metadata	~tens of GB	Titles, episodes, artwork — small, cacheable

Architecture overview

Content pipeline + serving

+--------+  upload   +-----------+  transcode   +---------+
| Studio |---------->| Ingestion |------------->| Origin  |
+--------+           +-----------+   (ladders)  +---------+
                                                      |
                                            +---------+---------+
                                            v                   v
                                  +-----------------+   +-----------------+
                                  | Open Connect    |   | Commercial CDN  |
                                  | (ISP appliances)|   | (overflow)      |
                                  +-----------------+   +-----------------+
                                            |                   |
                                            +---------+---------+
                                                      v
                                              +---------------+
                                              |  Client (ABR) |
                                              +---------------+

Uploads are write-cold; playback is read-hot. The CDN absorbs the read load.

Step-by-step request flow

Upload: a source video is uploaded via resumable upload to the ingestion service.
Transcode: a transcoder farm encodes the title into a ladder of resolutions/bitrates (240p -> 4K) and packages segments as HLS/DASH.
Distribute: segments land in the origin and are proactively pushed to edge caches (Open Connect appliances inside ISPs).
Playback: the client fetches a manifest, then requests segments; adaptive bitrate (ABR) switches rungs as throughput changes.
Resume: the playback service records the resume point; on a new device, the client seeks to it.

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