Adaptive Bitrate Streaming: How It Works and Why It Matters

February 12, 2019 by
Adaptive Bitrate Streaming for Multi-Device Delivery   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 as 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.  

Shirtless Adam Levine: Brought to You by ABR

Despite attracting one of the lowest television audiences in years, a game-changing seven million viewers streamed this year’s Super Bowl. Well, the viewership wasn’t actually game-changing. A winning record was in Tom Brady’s favor from the get-go. But the real MVP was adaptive bitrate streaming. Why? This marked a 70 percent increase in streaming spectators from 2018. And these viewers weren’t tethered to their couches, either. Some were streaming the game on a laptop while waiting to board a delayed flight. Others were hiding from the Polar Vortex in a ski lodge with the game on their cell phones. And some were on the beach in Cabo squinting at a sandy iPad. Even so, the streams made it to their screens with minimal buffering and near-real-time delivery. So what’s the Super Bowl have to do with adaptive bitrate streaming? In 2019, everything. Different screens and varying internet speeds were no match for Adam Levine’s bare chest. Both mobile devices and 4K home theaters displayed adequate-enough streams to entice seven million viewers. 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 2019 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. Adaptive Bitrate Streaming for Multi-Device Delivery 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 the 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 Streaming Engine™ software or Wowza Streaming Cloud™ service. 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   
235 320×240
375 384×288
560 512×384
750 512×382
1050 640×480
1750 720×480
2350 1280×720
3000 1920×720
4300 1920×1080
5800 1920×1080

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, RTMP (Real-Time Messaging Protocol) 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 is at its zenith. 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 Streaming Cloud™ service 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.   Endnotes:
  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 content delivery. In addition to writing, Traci enjoys cooking, reading, gardening, and spending quality time with her fur babies. Follow… View more