Overview
The AWS re:Invent conference is the premier event for Amazon Web Services, showcasing keynote speeches that captivate audiences globally. The live streams of these keynotes are a highlight for the AWS Event Technology Team each year. In 2018, AWS Elemental unveiled a cutting-edge video encoding mode known as QVBR (Quality-defined Variable Bitrate). This advanced encoding technique adapts video bitrate based on content complexity while ensuring a consistent quality is achieved with minimal bitrate usage.
Traditional variable bitrate encoding does address some issues associated with constant bitrate methods, allowing for higher bitrates during complex scenes and lower ones for simpler segments. However, it still requires an operator to select an average bitrate, potentially wasting bits on scenes where they do not enhance visual quality. QVBR enhances this process by optimizing bit usage while maximizing quality.
After initial tests, the AWS Event Technology Team recognized the advantages of QVBR and opted for its implementation across all live keynote streams at re:Invent in November 2018. This marked a departure from the constant bitrate encoding previously utilized.
Why the switch? During testing, the team observed a notable improvement in visual quality alongside a reduction in bandwidth consumption with QVBR enabled. Given the investment in high-quality visuals, production tools, and artwork, adopting QVBR to compress and deliver the event in conjunction with AWS Elemental and other AWS tools significantly enhanced the viewer experience.
Broadcasting the re:Invent Keynotes
The keynote broadcasts at re:Invent posed substantial encoding challenges due to high-resolution backgrounds and musical performances. QVBR alleviates the complexities of managing a “bits budget” by intelligently allocating bitrate; it uses more bits during complex shots and conserves them when the desired quality is achieved. This makes it straightforward to turn on QVBR for any type of source content without adjusting settings for different types of live or file-based content.
The implementation of QVBR for re:Invent’s live streams was a success. Transitioning from CBR to QVBR did not affect performance since this rate control mode is integrated into the live encoder. Viewer feedback regarding picture quality and stream reliability—especially on less-than-optimal WiFi networks—was overwhelmingly positive.
Remarkably, audience numbers for the live keynotes surged in 2018 compared to the previous year, and streaming costs dropped by over 20%. By adopting QVBR, the quality of the video improved while simultaneously reducing costs associated with CDN and storage—a true win-win scenario. Due to this success, QVBR will continue to be utilized by the AWS Event Technology Team.
For those interested in re-watching any of the re:Invent keynotes, you can find them here.
Implementing QVBR for Your Live or On-Demand Video
QVBR is accessible through several AWS Elemental live and file-based products:
- AWS Elemental Live (hardware and software encoder for live content)
- AWS Elemental Server (hardware and software encoder for file-based content)
- AWS Elemental MediaLive (AWS Cloud service for encoding live content)
- AWS Elemental MediaConvert (AWS Cloud service for encoding file-based content)
There is no additional cost or licensing needed to use QVBR in these products. For MediaLive and MediaConvert, the QVBR feature is ready for immediate use. Users of AWS Elemental Live or AWS Elemental Server may need to update their software to access QVBR.
To configure QVBR for the live keynotes at re:Invent, the following screenshots depict its activation in both AWS Elemental Live and AWS Elemental MediaLive. While the configuration for file-based products, AWS Elemental Server and AWS Elemental MediaConvert, is not shown here, it follows a similar process, and the quality setting guidelines outlined below apply.
In AWS Elemental Live, QVBR can be found in the Rate Control Mode selector:
- Rate Control Mode set to QVBR in Event settings.
Utilize the QVBR quality level setting to determine the quality standard for the stream, where 10 is the highest.
For AWS Elemental MediaLive, the QVBR encoding mode is integrated into the Stream Settings area, under Rate Control:
- In Stream Settings, find QVBR in the Rate Control dropdown menu.
Selecting the Right QVBR Quality Level
Once QVBR is selected, the primary setting to adjust is the quality level, which ranges from 1 to 10. To determine the best quality level, consider the target display:
- Level 10: for archival use—targets very high (visually-lossless) quality.
- Level 9: for television or large displays.
- Level 8: for television or desktop displays.
- Level 7: for desktop or tablet displays.
- Level 6: for smartphone or small display devices.
- Levels 5 – 1: for very small mobile displays with low bitrate requirements.
When employing QVBR with ABR (adaptive bitrate) sets for content delivery, such as HLS or DASH formats, each rendition can utilize different quality settings. Moreover, QVBR is compatible with the AVC (H.264) codec and the more efficient HEVC (H.265) codec, allowing a migration to HEVC together with QVBR for enhanced bit savings.
The demonstration of QVBR below illustrates the significant savings achievable.
As shown in the real-time graph below, there are notable bit savings with QVBR compared to CBR mode for both quality levels 8 and 7. During a specific period, the QVBR bitrates dropped considerably while maintaining nearly the same quality as the higher CBR bitrate, resulting in smaller file sizes and direct cost reductions for storage (for archived content) and delivery (CDN data transfer).
For more insights about QVBR, check out this blog post and learn from the experts here, they are an authority on this topic. Also, for those interested in further resources, explore this excellent resource.
Give QVBR a try during your next live event or while transcoding your content!
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