What Is Adaptive Bitrate Streaming & How Does It Work?

Adaptive bitrate streaming is a method used by internet broadcasters to provide a seamless streaming experience. If you’ve ever watched a livestream where image quality shifts between different resolutions and bitrates depending on the quality of your connection, you’ve witnessed adaptive bitrate streaming at work. All major streaming platforms, including YouTube and Twitch, use adaptive bitrate streaming.

Knowing how adaptive bitrate streaming works is important for livestreamers and video content creators because it helps you understand how different viewers experience your content.

Here is everything you need to know about adaptive bitrate streaming.

What is Adaptive Bitrate Streaming?

Adaptive bitrate streaming is a streaming technique where a single media source is encoded at multiple bitrates.

This allows viewers (specifically their media players) to dynamically switch between different encodings in real time depending on available resources (mainly CPU and available bandwidth). Adaptive bitrate streaming allows viewers to enjoy the content in the highest possible quality and as efficiently as possible.

Adaptive Bitrate Streaming Vs. Progressive Streaming

To understand adaptive bitrate streaming, it’s helpful to start by understanding the differences between adaptive bitrate streaming and progressive streaming.

Progressive streaming is not technically streaming at all. It is a form of content delivery where the viewer downloads an entire media file to their device. Some people confuse it with streaming because progressive download allows viewers to start watching the file as it downloads (hence the name).

Unlike adaptive bitrate streaming, progressive download doesn’t allow switching between different encodings. You can only download a single media file that has been encoded at a fixed bitrate.

The downside to progressive streaming is that viewers may encounter buffering or lower quality video depending on their network connection and CPU power. If you’re watching a 720p video on a 1080p screen, it will get pixelated due to scaling. On the other hand, if you’re watching a 1080p video over a public Wi-Fi connection, you might experience buffering lag because it takes more bandwidth to download a larger 1080p file.

Adaptive bitrate streaming was initially developed to circumvent these issues.

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How Does Adaptive Bitrate Streaming Work?

Adaptive bitrate streaming has several different software implementations. The most widely used are MPEG-DASH and HLS, but there are others like Microsoft Smooth Streaming, Adobe HTTP Dynamic Streaming, and Uplynk.

Each implementation uses a similar procedure, which can be described in the following way:

1. The media source is split into short, 1 to 10-second segments.
2. The encoder creates encodings with different bitrates for each segment.
3. The segments are indexed and arranged into playlists or profiles (more on that later), one for each bitrate.
4. The media player receives the playlists (typically in a header file).
5. The media player switches between different playlists in real time based on current bandwidth and CPU load.

Let’s illustrate with an example.

You start watching a livestream by one of your favorite Rust streamers or Minecraft streamers. You’re watching from a phone through a public Wi-Fi connection. Your phone supports a 1080p resolution, so your media player defaults to a high-bitrate for the stream.

Suddenly, the Wi-Fi signal drops in quality. Your media player detects a change in available bandwidth, and switches to a lower-bitrate playlist, which downgrades the stream resolution to 720p. The Wi-Fi then goes back to normal, and your media player switches back to the high-bitrate version of the stream.

All of this happens automatically in the background thanks to adaptive bitrate streaming.

Besides adapting to slow buffering speeds, adaptive bitrate streaming helps videos look good on any device. Since the resolution can vary, adaptive bitrate streaming allows the video player to pick the resolution that best suits the device.

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Adaptive Bitrate Streaming Profiles

Adaptive bitrate streaming techniques can encode segments at any bitrate. In practice, there are several different tiers or profiles that most streaming services use. Apple, the developer of the HLS adaptive bitrate protocol, proposed a fixed bitrate encoding ladder with 10 different quality variants, which you can find in the table below.

Network Type	Dimensions (pixels)	Frame Rate	Total Bitrate (kbps)	Audio Bitrate (kbps)	Keyframe
Cell	480×320	n/a	64	64	n/a
Cell	416×234	10-12	264	64	30 to 64
Cell	480×270	12-15	464	64	90
WiFi	640×360	29.97	664	64	90
WiFi	640×360	29.97	1264	64	90
WiFi	960×540	29.97	1864	64	90
WiFi	960×540	29.97	2564	64	90
WiFi	1280×720	29.97	4564	64	90
WiFi	1280×720	29.97	6564	64	90
WiFi	1920×1080	29.97	8564	64	90

Other streaming companies such as Netflix proposed their own streaming profile ladders.

Benefits of Adaptive Bitrate Streaming for Streamers

Thanks to adaptive bitrate streaming, streamers and other content creators only need to provide a single, high-quality content source, and leave it to streaming platforms and media players to figure out which version to display. This ensures that each viewer has the best possible viewing experience, irrespective of which device they’re using, or the kind of internet connection they have.

Conclusion

From a content creator perspective, adaptive bitrate streaming has been a huge quality of life improvement. It ensures a consistent viewing experience, and all the work needed to make it happen occurs in the backend. All you have to do is pick a livestreaming platform for gaming or video that supports adaptive bitrate streaming, and you’re done.

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