Adaptive Bitrate Streaming: How It Works and Why It Matters

February 9, 2021 by
Laptop and mobile phone playing live video stream.

Adaptive bitrate streaming provides the best video quality and viewer experience possible — no matter the connection, software, or device. Called ABR for short, the majority of these streams are delivered via HTTP-based technologies such a MPEG DASH and Apple’s HLS.

In this blog, we’ll discuss why adaptive bitrate streaming matters and how it works. But first, let’s segue into the details by looking at one of the most-watched live broadcasts in the United States: the Super Bowl.


Andy Reid’s Mask: Brought to You by ABR

Between the Bruce Springsteen Jeep commercial and Biden’s plea for Americans to continue social distancing, this year’s Super Bowl was an unusually introspective event. It was also an awkward one — much like the past 13 months have been.

What, specifically, made it awkward? Well, Andy Reid’s mask for one thing.


The grim reality of the COVID-19 pandemic only added to the awkwardness. Whereas the Super Bowl has traditionally served as an excuse to get together with family and friends, most of us celebrated this year’s game in isolation… far away from family and friends. 


Expressions like ‘in these uncertain times’ and ‘together but apart’ popped up throughout the broadcast, adding even more sentimentality to the event. And that, in turn, interrupted the fanfare. After all, most of us were tuning in for a distraction from reality, not a microcosm of it.

But even so, the strangeness of Super Bowl LV was appropriate. In a Time’s article titled The Pandemic Super Bowl, Naturally, Was Rough to Watch, Sean Gregory writes:

“It all felt weird. Despite the best efforts of all involved, from players to TV producers, things were off all night… Let’s hope for a return to Super Bowl spectacle in the years ahead.”


Streaming Viewership at an All-Time High

Despite all of this, a game-changing average of 5.7 million viewers per minute streamed this year’s Super Bowl — making it the most live streamed NFL game of all time.

Well, the viewership wasn’t actually game-changing. A winning record was in Tom Brady’s favor from the get-go.


But regardless of whether you were rooting for or against the GOAT, the real MVP was adaptive bitrate streaming.

Why? This marked a 65 percent increase in streaming spectators from 2020. Due to the pandemic, fewer fans were at the stadium than ever before, and many of us avoided watching the game at a crowded party.

Viewers weren’t tethered to their couches, either. Some were streaming the game on a laptop while self-quarantined from their family. Others were braving the airport with the game on their cell phones. And some were on the beach in Florida, where they’ve been working remotely all winter, squinting at a sandy iPad.

Even so, the streams made it to their screens with minimal buffering and speedy delivery. Some viewers even utilized interactive “watch party” features within their streaming platform to remain virtually connected with friends during the game.

Computer screen with live football broadcast, as well as interactive real-time chat and video between viewers

So what does the Super Bowl have to do with adaptive bitrate streaming? When it comes to Sunday’s pandemic-shaded broadcast, everything.

Different screens and varying internet speeds were no match for the NFL and CBS. Both mobile devices and home theaters displayed adequate-enough streams to entice the largest live streaming audience yet. Adaptive bitrate streaming provided a solid user experience despite varying conditions.


Why Does Adaptive Bitrate Streaming Matter?

Thanks to adaptive bitrate technology, streams of the 2021 Super Bowl dynamically adapted to fit the screen size and internet speed of everyone watching. Mobile viewers with poor connections didn’t have to wait for the game to load. For those plugged into high-speed internet, a higher resolution alternative played.

To connect with users — no matter where they are — you need adaptive bitrate streaming.

That way, you can deliver high-quality streams to users with outstanding bandwidth and processing power, while also accommodating those lacking in the speed and power department.

Rather than creating one live stream at one bitrate, a transcoder is used to create multiple streams at different bitrates and resolutions. This is easily done with a media server software.

Multiple renditions allow for playback on different bandwidths. The media server then sends the highest-quality stream possible for each viewer’s device and connection speed. And this is all done in the most efficient manner possible.

The result? No buffering or stream interruptions. Plus, as a viewer’s signal strength goes from two bars to three, the stream dynamically adjusts to deliver a superior rendition.

Adaptive bitrate streaming is vital to anyone trying to reach their target viewers. Why? Because viewers no longer notice it. They simply expect it.


How Does Adaptive Bitrate Streaming Work?

To optimize the viewing experience across a variety of devices and connection speeds, you’ll need a transcoding solution like the Wowza Video platform or Wowza Streaming Engine software.

Transcoding allows you to create multiple files from a single source through the process of transrating and transizing.

Let’s break down that trio of Ts:

  • Transcoding: An umbrella term for taking a compressed/encoded file and decompressing/decoding it to alter it in some way. The manipulated file is then recompressed for delivery. Transrating and transizing are both subcategories of transcoding.
  • Transrating: Changing the bitrate of the decompressed file to accommodate different connection speeds. This can include changing the frame rate or changing the resolution.
  • Transizing: Resizing the video frame — or resolution — to accommodate different screens.

Transrating and transizing are critical to adaptive bitrate streaming. The two also overlap. For example, taking a 4k video input stream at 13 Mbps and converting it to a 1080p stream at 4300 kbps would be an example of both transrating and transizing.


Dynamically Adapting for Multi-Device Delivery

The spectrum of transcoded files created would then fall on an encoding ladder. At the top, a high-bitrate, high-frame-rate, high-resolution stream is output for viewers with the highest-tech setups. At the bottom of the ladder, the same video in low quality is available viewers with small screens and crappy service.

Bitrate (kbps)    Resolution   

Netflix’s Traditional Bitrate Ladder

The transcoder breaks these renditions into chunks that are 2-10 seconds in length. These allow the player to dynamically shift between the different encodings depending on available resources.

The video player can then use whichever rendition is best suited for its display, processing power, and connectivity. If power and connectivity change mid-stream, the video will automatically switch to another step on the ladder.

It’s worth noting that adaptive bitrate streaming also helps minimize distribution costs. By limiting the bandwidth required to deliver streams across a content delivery network (CDN), distributors optimize connectivity expenses.

Adaptive Bitrate Streaming to Multiple Devices

The Rise of Adaptive Bitrate Streaming

In the early days, the Real-Time Messaging Protocol (RTMP) was the go-to method for streaming over the internet. Sending linear streams via RTMP enabled lightning-fast video delivery. That said, the protocol encountered issues getting through firewalls.

RTMP streams were encoded at a bitrate that was comfortably less than the bandwidth of target viewers. These were then delivered via a dedicated streaming server as a continuous stream of data.

The industry eventually shifted in favor of HTTP-based (Hypertext Transfer Protocol) technologies. These streams were not technically “streams.” Rather, they were progressive downloads sent via regular web servers.

This delivery method works by downloading the video as you watch it. The content could be cached on local servers and encountered less trouble getting through firewalls. But, this didn’t optimize for screen size or connectivity.

Then came adaptive bitrate streaming. Content distributors encoded streams into many different bitrates and broke them into fragments. These multi-bitrate chunks would then be indexed in a manifest file and delivered to the player.

The result? Very little buffering, fast start time, and a good experience for both high- and low-end connections.

Unlike progressive download, where the user would have to wait for the video to buffer if encoded at too high of a bitrate, adaptive bitrate streaming switches dynamically behind the scenes, without any user interaction.

As mentioned, the majority of ABR streams today are delivered via HTTP-based technologies such as MPEG-DASH and Apple’s HLS. RTMP streams can also be configured for adaptive bitrate streaming, but it’s not nearly as easy.


Adaptive Bitrate Streaming and Wowza


We’ve said it before and we’ll say it again: The streaming industry’s influence on everyday life continues to grow.

Video will make up 82 percent of all IP traffic by 2022, a growing share of which will take the form of live streaming.¹

Ever-increasing connectivity and more sophisticated technology have heightened customer expectations. Nobody’s going to stick around when faced with the dreaded buffering icon.

Luckily, adaptive bitrate streaming is easy. You can use the Wowza Streaming Engine software for adaptive bitrate delivery using your own servers — whether they’re on premises or in a third-party cloud platform. For those who want to get up and running quickly without any hassles, the Wowza Video platform might be a better fit.

It’s up to you: adapt or get out. Just make sure you start with adaptive bitrate streaming. And Wowza.


  1. Source: Cisco, Cisco Visual Networking Index: Forecast and Trends, 2018-2022

About Traci Ruether

As a Colorado-based B2B tech writer, Traci Ruether serves as Wowza's content marketing manager. Her background is in streaming and network infrastructure. Aside from writing, Traci enjoys cooking, gardening, and spending quality time with her kith and kin. Follow her… View more