AWS Media Blog

How-to: Use QVBR for Streaming Live Events Like the 2018 AWS re:Invent Keynotes

Introduction

AWS re:Invent is the largest event of the year for Amazon Web Services and the keynote addresses are the centerpieces of the week-long event. Live streams from re:Invent command a large viewership from around the world and are the highlight of the year for the AWS Event Technology Team.

In 2018, AWS Elemental introduced a new video encoding mode called QVBR (Quality-defined Variable Bitrate). QVBR is an enhanced version of variable bitrate control that scales video bitrate to maintain consistent video quality and match video complexity, while using the minimum bitrate required to reach a set quality level. Variable bitrate video encoding by itself offers a solution to the challenges when using constant bitrate video encoding – allowing a higher bitrate to be used during complex segments of video and a lower bitrate to be used during less complex segments. However, variable bitrate encoding presents its own set of issues: an operator needs to pick the desired average bitrate for an asset and the encoder consequently uses as many bits as required to hit the average bitrate, even if these extra bits don’t increase visual quality. QVBR encoding takes variable bitrate encoding a step further and is an even more adaptable method of reducing wasted bits while keeping video quality as high as possible.

After some initial testing, the AWS Event Technology Team clearly saw the benefits of QVBR and decided to implement it into all live keynote streaming at re:Invent in November, 2018. This was a shift from the constant bitrate encoding used in the past and what is commonly used today in live streaming.

So why change? The team noted during testing an appreciable increase in visual quality while also seeing a clear savings in bandwidth with QVBR enabled. The show, like most large live events, invests in high-quality visuals, production tools, and artwork to deliver valuable information to AWS customers. Using QVBR to compress and deliver the event with additional AWS Elemental and AWS tools created a better experience for viewers than ever before.

Amazon Web Services CEO, Andy Jassy, on stage for his keynote at re:Invent 2018

Broadcasting the re:Invent keynotes

The re:Invent keynote broadcasts represent difficult encoding challenges such as the large, high-resolution displays behind the speakers and the musical acts. QVBR eliminates the guesswork and frustration of managing a “bits budget”: when shots from the event are more complex, QVBR spends more bits to maintain the desired video quality level. When the video quality level is reached, QVBR does not spend any extra bits. It’s simple to turn QVBR on and then process any type of source content, without the need to adjust settings for different types of live (or file-based) content.

With QVBR enabled, the live streams from re:Invent were a great success. Switching from CBR to QVBR had no impact on performance as the rate control mode is built into the live encoder itself. And the feedback from viewers about picture quality and the reliability of the streams (even on less than optimal WiFi networks) was very positive.

Even more incredibly, the audience watching the live keynotes grew significantly in 2018 compared to the previous year. However, the overall cost of streaming dropped by over 20%. By moving to QVBR, the video quality can be raised while at the same time the cost (for things like CDN and storage) can be lowered – truly a win-win result.

Given this success, QVBR is a feature that will be used in the future by the AWS Event Technology Team.

If you would like to re-watch any of the re:Invent keynotes, you can find them here: https://live.awsevents.com/previous/

re:Invent 2018 Keynote

How to use QVBR with your live or on-demand video

QVBR is available in several AWS Elemental live and file-based products and services:

In all of these products and services, there isn’t any extra cost or licensing for using QVBR. With MediaLive and MediaConvert, the QVBR feature is ready for you to use today. If you are using the AWS Elemental Live or AWS Elemental Server products, you may need to update your software to the latest release to enable access to QVBR.

For the live keynotes at re:Invent, the following screenshots demonstrate where we enabled QVBR in both AWS Elemental Live and AWS Elemental MediaLive. Configuring QVBR in the file-based products, AWS Elemental Server and AWS Elemental MediaConvert, while not shown here is similar to the process below, and choosing the right quality setting guidelines below still apply.

In AWS Elemental Live, QVBR is available in the Rate Control Mode selector:

AWS Elemental Live encoder showing Rate Control Mode set to QVBR in the Event settings

 

Use the QVBR quality level setting to choose the quality standard for the stream, where 10 is the highest quality

If you’re using AWS Elemental MediaLive, QVBR encoding mode is found in the Stream Settings area, under Rate Control:

Using AWS Elemental MediaLive, in Stream Settings you will find QVBR in the Rate Control dropdown menu

Choosing the right QVBR Quality Level

Once you select QVBR, the main setting to configure is the quality level, which runs on a scale from 1 to 10. The best way to think about quality level is to use the target display as a guide. The recommended values according to display devices are:

  • Level 10: for archival use, this setting targets very high (visually-lossless) quality
  • Level 9: television or other large displays
  • Level 8: television or desktop computer displays
  • Level 7: desktop or tablet displays
  • Level 6: smart phone or other small display devices
  • Levels 5 – 1: very small mobile displays with very low bitrate requirements

When using QVBR with ABR (adaptive bitrate) sets for delivering content, such as HLS or DASH formats, each rendition can use a different quality setting. Additionally, QVBR works with the AVC (H.264) codec and also the more efficient HEVC (H.265) codec, so you can use migrate to the HEVC codec along with QVBR to further increase your bit savings.

The example demonstration of QVBR below highlights the tangible savings that are possible.

As you can see from the real-time graph running at the bottom, there is dramatic bit savings with QVBR compared to CBR mode for both the quality level 8 and 7 QVBR encodes. During a stretch of time in the middle of the match, the QVBR bitrates dropped significantly while the quality remained almost identical to the higher CBR bitrate, with the smaller file sizes resulting in direct cost savings on storage (for the archived version) and delivery (CDN data transfer).

Learn more about QVBR and try it yourself

To learn more about QVBR, please visit: https://www.elemental.com/applications/what-quality-defined-variable-bitrate-qvbr-control

You can also watch the “Introduction to QVBR” webinar here: https://www.elemental.com/resources/webcasts/intro-qvbr-quality-defined-variable-bitrate-control

Give QVBR a try on your next live event or when transcoding your on-demand videos and see the results for yourself!

Josh Winstead

Josh Winstead

Emmy and HPA Award winning broadcast professional with an expertise in broadcast engineering, operations and streaming media. I'm currently a Technical Marketing Engineer with AWS Elemental.