How Does Netflix's System Support Millions of Simultaneous Live Viewers?

Recently, Alex Honnold free-soloed to the top of Taipei 101 without any safety equipment, sparking global discussion. As software engineers watching the livestream with sweaty palms, it's natural to wonder: "How does Netflix's infrastructure handle millions of viewers watching simultaneously?" Checking the facts, Netflix's most-watched livestream had over 65 million concurrent viewers—a staggering number.

While we haven't built a live streaming platform ourselves, Netflix's official tech blog has published numerous articles on live streaming engineering. Through this article, we'll explore Netflix's engineering team's approach to understand the technical insights behind their success.

What Technical Challenges Does Live Streaming Create Compared to On-Demand?

Before diving into Netflix's live streaming architecture, we should ask: "Netflix's on-demand streaming already performs exceptionally well in throughput, latency, and reliability—what additional technical challenges does live streaming present that on-demand can't solve?" In other words, even though live events attract tens of millions of viewers, popular on-demand releases (like the Squid Game phenomenon) draw similarly massive audiences. Why is live streaming technically more challenging?

Live streaming requires completing capture, encoding, and transmission in extremely tight timeframes while maintaining real-time performance and low latency—no easy feat. The viewing patterns also differ significantly. Live streams can experience sudden traffic spikes from unexpected events (imagine a celebrity posting that they're watching, causing viewers to immediately switch over). With on-demand content, there's less urgency to watch immediately.

For buffering, on-demand services can pre-load entire content; live streams cannot. The buffer window is much smaller. Because live streams happen in real time, viewers have lower tolerance for errors (most people can't accept streaming interruptions), creating significant operational pressure for the team.

Understanding these distinctions helps us see how Netflix's team architected their response.

Overall Architecture

Netflix's live streaming architecture breaks down into three main components:

• Content Acquisition: Live streams originate from cameras and audio equipment. The captured content enters an operations center for basic quality checks (signal integrity, content validation). Netflix mentioned Alex Honnold's stream had a 10-second delay—if something went wrong, the feed could be cut immediately at this stage.
• Real-Time Stream Processing: After passing validation, video undergoes transcoding to ensure compatibility across different user devices. The content is then packaged for seamless integration with the playback system.
• Global Distribution: The processed live content is distributed via CDN from origin servers to edge servers worldwide, allowing viewers to fetch from the nearest server and minimize latency.

Ensuring Availability

Live streaming must handle diverse devices (TV apps, web apps, mobile apps) with varying format support, and diverse network conditions (low speeds and instability in developing regions).

To ensure smooth playback regardless of device or network speed, transcoding is essential. Netflix captures live events with high-end cameras producing ultra-high resolution footage. Without transcoding into multiple formats and bitrates, older devices might not play the content and slow networks couldn't download it.

A critical element in Netflix's architecture is redundancy. To avoid single points of failure, Netflix maintains two independent network connections for receiving signals, with independent transcoding and packaging. If one path experiences network issues or equipment failure, the backup provides protection.

Minimizing Latency

When discussing latency, we must address transmission protocols. Many assume UDP would be better than TCP for speed since UDP discards lost packets and transmits faster, while TCP retransmits lost packets for reliability, making it slower.

Yet Netflix chose HTTP (TCP-based), not UDP. Several reasons support this choice. First, live broadcast quality matters—Netflix prioritizes stable, high-quality streams. UDP might cause frame drops, which they want to avoid. Second, HTTP enjoys near-universal device support, enabling compatible encoding and distribution.

Netflix reduces latency through segmentation: breaking content into small chunks for transmission. Specifically, Netflix uses 2-second segment durations. Encoders transmit each 2-second segment immediately upon generation—the playback client can consume it without waiting for the entire segment to finish encoding.

Of course, this choice has tradeoffs. Longer segments compress more efficiently, reducing server load. But balanced against these factors, 2-second segments ensure stable, frame-drop-free streams while achieving industry-standard latency.