how hls video streaming works

Video streaming platforms like Netflix, YouTube Live, and many OTT services use a streaming protocol called HLS (HTTP Live Streaming).

If you’ve ever wondered:

What is HLS video streaming?
How does HLS streaming work internally?
What is an m3u8 file?
How does adaptive bitrate streaming work?
How does Netflix stream videos smoothly?

This guide explains HLS video streaming step by step from a backend and system design perspective.

What is HLS video streaming?

HLS (HTTP Live Streaming) is a video streaming protocol developed by Apple that delivers video content over HTTP.

Instead of sending a full video file at once, HLS breaks the video into small chunks called segments.

Each segment is usually:

2 to 10 seconds long
Encoded in different quality levels
Delivered via standard HTTP

This allows video players to download and play video in small pieces rather than waiting for the entire file.

How HLS Video Streaming Works

The HLS streaming architecture works in the following steps:

1. Video Encoding

A video file is first encoded into multiple resolutions, such as:

240p
480p
720p
1080p

Each resolution is encoded separately.

2. Video Segmentation

Each encoded version is divided into small parts. ts (Transport Stream) segments.

For example:

segment1.ts
segment2.ts
segment3.ts

These segments are typically 4–6 seconds long.

3. m3u8 Playlist File

HLS uses a playlist file called an m3u8 file.

The m3u8 file contains:

List of segment URLs
Available video quality levels
Streaming metadata

There are two types of playlists:

Master Playlist → Lists all available quality streams
Media Playlist → Lists actual video segments

When a user opens a video, the player first downloads the m3u8 file.

4. Adaptive Bitrate Streaming

One of the most important features of HLS is adaptive bitrate streaming.

The video player continuously checks:

User internet speed
Network stability
Buffer health

If the network is slow:

The player switches to a lower resolution stream.

If the network improves:

The player switches to a higher resolution.

This switching happens automatically without interrupting playback.

This is why HLS video streaming works smoothly even on unstable connections.

HLS Streaming Architecture

The basic HLS streaming architecture includes:

Video Encoder
Segmenter
Web Server or CDN
Client Video Player

The workflow:

Video is encoded and segmented
m3u8 playlist is generated
Segments are uploaded to server or CDN
Client downloads playlist
Client fetches segments sequentially
Adaptive switching happens automatically

Because HLS uses HTTP, it works easily with CDNs and caching systems.

Why HLS Uses HTTP

HLS streaming uses HTTP instead of raw TCP or UDP streaming because:

HTTP works through firewalls
HTTP works with CDNs
HTTP is scalable
No persistent connection required
Easy to cache video segments

This makes HLS ideal for large-scale platforms like Netflix and live streaming services.

HLS vs DASH

Another common streaming protocol is DASH (Dynamic Adaptive Streaming over HTTP).

HLS vs DASH differences:

HLS was developed by Apple
DASH is an open standard
Both support adaptive bitrate streaming
Both use segmented video delivery
HLS is widely supported on Apple devices

Most platforms support both today.

Real-World Use Cases of HLS

HLS is commonly used for:

Live streaming platforms
OTT applications
E-learning platforms
Video-on-demand services
Sports streaming

Because of its scalability and adaptive bitrate capabilities, HLS is considered one of the most reliable streaming protocols.

Conclusion

HLS video streaming works by breaking video into small segments, delivering them via HTTP, and using adaptive bitrate streaming to adjust quality dynamically.

Key components of HLS:

m3u8 playlist
.ts segments
adaptive bitrate
HTTP delivery
CDN integration

Understanding how HLS streaming works is important for backend developers, system designers, and engineers building scalable video platforms.