# Video streaming

> Watching a video while it arrives in small pieces, instead of downloading it all first.

- Level: Basic
- Topics: Networks
- URL: https://tidbit.legios.com.ar/video-streaming/
- In Spanish: [Streaming de video](https://tidbit.legios.com.ar/es/video-streaming/)

**Video streaming** is how Netflix, YouTube or a live match reach your screen: the video starts playing after a moment, while the rest is still on its way. Behind the scenes, the video has been **compressed** with a codec such as H.264 or AV1, which shrinks it by storing only what changes from one frame to the next, and then cut into short **segments** of a few seconds each.

Each video is also prepared in several versions, from low resolution to 4K, each with a different **bitrate**: how many bits per second it needs. A small text file, the **manifest**, lists all the versions and segments. Your player reads it and requests the segments one after another over ordinary HTTP, usually from a CDN server near you, keeping a few seconds or minutes stored ahead in a **buffer**.

The clever part is **adaptive bitrate streaming**. The player constantly measures how fast segments are arriving. If your Wi-Fi slows down, it asks for the next segments in a lower quality, so the picture gets blurrier for a while but keeps moving; when the connection improves, it climbs back up. The spinning wheel of **buffering** appears only when the buffer runs empty faster than it can be refilled. HLS and MPEG-DASH are the two common formats for this, and live streams work the same way, with segments created on the fly a few seconds behind real time.

## An analogy

A conveyor belt of sushi plates. You start eating as soon as the first plate arrives, the kitchen keeps a few plates ahead of you, and if it gets busy it sends simpler dishes so you never sit in front of an empty belt.

## Keep in mind

- The video is compressed and cut into segments of a few seconds.
- Each video exists at several bitrates; a manifest lists them.
- The player switches quality segment by segment to match your connection.
- Buffering happens when the buffer empties faster than it refills.

## Go deeper

- [Adaptive bitrate streaming on Wikipedia](https://en.wikipedia.org/wiki/Adaptive_bitrate_streaming)
- [Streaming audio and video (MDN)](https://developer.mozilla.org/en-US/docs/Web/Media/Guides/Streaming)
- [Streaming media on Wikipedia](https://en.wikipedia.org/wiki/Streaming_media)

## Related terms

- [Netflix](https://tidbit.legios.com.ar/netflix/): A streaming service, and the engineering it built to deliver video to the whole world.
- [Display resolution](https://tidbit.legios.com.ar/display-resolution/): How many dots, or pixels, make up a screen's image: more dots, finer detail.
- [HTTP](https://tidbit.legios.com.ar/http/): The request-and-response language browsers and websites speak.
- [CDN](https://tidbit.legios.com.ar/cdn/): Copies of a website kept on servers around the world, close to whoever asks.
- [Server](https://tidbit.legios.com.ar/server/): A computer whose job is to answer requests from other computers, all day, every day.
- [Wi-Fi](https://tidbit.legios.com.ar/wi-fi/): Networking over radio waves: the internet without the cable, within a few rooms.