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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 (171 downloads)
