CBR, VBR and CQP: pick by where the video is going
Three settings, one dropdown, and the guidance online contradicts itself. The rule is simpler than it looks once you ask what the video has to survive.
Rate control answers one question. When a scene gets busy, does the encoder spend more bits or lower the quality?
Which answer you want depends on where the video goes next.
CBR, for anything live
Constant bitrate holds output steady. A still scene wastes bits padding. A busy scene gets the same allowance and drops quality to fit.
That sounds bad. It is what live needs. Your upload has a hard ceiling and the platform sizes its buffer against a predictable rate. A spike that overshoots your uplink becomes dropped frames, and dropped frames are worse than a soft second of video.
CQP and CRF, for recordings
Constant quality inverts the deal. You set a quality target and the bitrate goes wherever it needs to. Still scenes get small. Busy scenes get the bits.
Nobody is streaming the file, so nothing cares about the peaks. You get consistent quality and a smaller file than CBR at the same look. CQP is the NVENC name. CRF is the x264 name. Same idea.
Going down a pipe, use CBR. Going to a disk, use CQP or CRF. Going to an upload where the platform re-encodes anyway, use VBR with a cap.
VBR, and why live is not its job
Variable bitrate targets an average and allows peaks. Good for a file you will upload once.
On a stream the peaks are the problem. Your uplink does not care about your average. It cares about the worst second, and that is when the encoder decided the scene deserved triple bitrate.
The setting nobody adjusts
CBR still has a buffer. Its size decides how tight the rate stays. A buffer equal to one second of video keeps output tight. A larger buffer allows short overshoots and looks better on hard cuts.
Most people leave it at the default and never learn it exists. Leave it alone unless you are chasing dropped frames on a marginal uplink, and then bring it down.
What to set
| Destination | Mode | Why |
|---|---|---|
| Live stream | CBR | Predictable for your uplink and the platform buffer. |
| Local recording | CQP or CRF | Consistent quality, smaller files, no ceiling to respect. |
| Upload to a video platform | VBR with a max | They re-encode. Give them a clean source without a silly peak. |
| Archive master | CRF, low number | Quality now costs disk. Quality later costs the footage. |
Sources
- OBS Studio, application overview
- FFmpeg documentation
- NVIDIA video encode and decode GPU support matrix
The Rig Wire reports on streaming technology from public documentation, source repositories and vendor releases. We did not bench-test what is described here. When we have tested something, we say so.