Adaptive Bitrate: The QoE Evolution of Connectedness

1st March, 2017 by

We live in an age when a home can have numerous devices attempting to upload and download data through one overburdened broadband connection. From IoT-enabled smart devices to automatically-updating tablets and phones, connection speeds can be under strain. This is before people start streaming content or playing games online.

It’s common for one household to have multiple subscriptions with different OTT providers, while offline games are becoming something of a rarity.

Protecting Your Continuity

Viewed in this way, it’s easy to see why packet loss and latency are such major issues. Technology normally outpaces our ability to harness it effectively, yet when it comes to internet connectivity, the opposite is true. Our overburdened cellular and landline networks simply can’t cope with the 20% year-on-year rise in US internet traffic, so the provision of dependable HD video streaming would be impractical unless consumers were watching through the night. That clearly doesn’t work, given the on-demand business model of this burgeoning industry.

Adaptive bitrates represent a partial workaround to this conundrum. The basic principle is that a live or pre-recorded transmission is broken into segments of between two and four seconds. Each segment is then encoded at several different bitrates of varying size and quality.

The lowest bit rate will result in pixelated, yet compact packets of data, while the highest will feature the best picture quality that output devices can realistically handle – like 1080p. A manifest file will catalog all the different packets and varying bitrates, ensuring that segments are always distributed in the correct order even if the quality is constantly changing. This is delivered first, so the client device knows the program’s length, resolutions and DRM in advance.

Streaming Without Interruption

When a user begins streaming, their client device will automatically select the lowest bitrate from the host server. That’s why streamed content often appears pixelated to begin with, but also why programs can start playing within seconds of being selected.

From this point on, the client device is constantly monitoring available internet bandwidth and system resources. If it detects that the download speed has exceeded the initial segment’s bitrate, and a buffer of available data can be maintained, subsequent segments will be requested at a higher quality. This process continues throughout the transmission, constantly outputting the highest picture quality network resources will allow while responding in real time to fluctuations in bandwidth.

The Perfect Technological Storm

The early years of this decade saw several proprietary implementations of adaptive bitrate streaming being developed, including Adobe’s Dynamic HTTP Delivery and Microsoft Smooth Streaming. However, these have been eclipsed by the first international standard for adaptive bitrates – the Moving Picture Expert Group’s Dynamic Adaptive Streaming over HTTP. Better known as MPEG-DASH, this uses standard HTTP distribution and fragmented MP4 files to ensure compatibility with the vast majority of internet-enabled devices.

Following a successful trial at the 2012 London Olympics, DASH has quickly become the default method streaming providers use to offer their content across today’s spectrum of devices, from phones and tablets to games consoles and desktop computers.

The Race Is On, Apple Running A Close Second

The only significant rival to MPEG-DASH comes, perhaps inevitably, from Apple. Even Apple’s HTTP Live Streaming is inching towards compatibility with its rival, however, following the recent adoption of fragmented MP4 compatibility. Analysis of MPEG-DASH’s technical abilities also shows how its collaborative development by historic rivals (including Dolby, Adobe, Microsoft and Samsung) has enabled it to outperform alternative systems like Smooth Streaming.

DASH is the only platform with HTML5 support, the only one that is agnostic to video and audio codecs, and the only one capable of client logging and reporting. It seems reasonable to assume that this will become the dominant format relatively soon, especially given HLS’s less efficient splicing of data chunks and smaller target audience (Apple hardware users).

Moving Forward Into The Bandwidth

The aim of adaptive bitrate technology is to give viewers the highest quality output without the stuttering and freezing caused by buffering. Interruptions to programming are the nemesis of any streaming service, and content providers are often blamed even when the cause is beyond their control. Until 5G and Li-Fi or ultrafast broadband enable us to distribute data without fear of encountering bandwidth congestion, adaptive bitrates will continue to represent a vital workaround to the challenges of our inadequate legacy communications infrastructure.