Compares the quality of Constrained VBR and Capped VBR

Best SVT-AV1 Bitrate Control Technique for Live Streaming

There are four bitrate control techniques worth considering for live encoding/transcoding using the SVT-AV1 codec. These are:

  • Capped CRF
  • VBR
  • Capped VBR
  • Constrained VBR

Here’s what I found: Overall:

  • Capped CRF shows promise with significant bitrate savings, good quality retention, and the best overall performance by ~10 – 25% (meaning more streams from the same hardware).
  • VBR was generally the best of the three VBR variants.
  • Capped VBR was very similar to VBR with no significant advantages (again, in the live use case).
  • Constrained VBR produced a more consistent bitrate, but had:
    • The highest peak bitrates (potential deliverability issues).
    • The lowest average VMAF score of the three VBR variants.
    • The lowest low-frame quality scores, indicating the potential for transient quality issues.
  • Bottom line: Either use VBR or capped CRF.

You can download a report detailing these findings here. No registration is required.

SVT-AV1 Bitrate Control Modes for Live Streaming (813 downloads )

About Jan Ozer

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I help companies train new technical hires in streaming media-related positions; I also help companies optimize their codec selections and encoding stacks and evaluate new encoders and codecs. I am a contributing editor to Streaming Media Magazine, writing about codecs and encoding tools. I have written multiple authoritative books on video encoding, including Video Encoding by the Numbers: Eliminate the Guesswork from your Streaming Video (https://amzn.to/3kV6R1j) and Learn to Produce Video with FFmpeg: In Thirty Minutes or Less (https://amzn.to/3ZJih7e). I have multiple courses relating to streaming media production, all available at https://bit.ly/slc_courses. I currently work as www.netint.com as a Senior Director in Marketing.

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