Concept · Encoding concepts
VBR vs CBR: Which Bitrate Mode Should You Use?
Constant bitrate is a fixed data rate; variable bitrate spends bits where the picture needs them. CBR is a delivery constraint, VBR is a quality optimization — and confusing the two causes most encoding waste.
The one-paragraph difference
CBR (constant bitrate) keeps the data rate flat at all times, padding easy scenes to hit the target. VBR (variable bitrate) allocates more bits to complex scenes and fewer to static ones — the same average rate, but with quality concentrated where it matters.
Side by side
| CBR | VBR | |
|---|---|---|
| Bitrate over time | Flat (padded) | Varies with scene complexity |
| Quality | Drops on complex scenes | Consistent quality per scene |
| File size | Predictable | Predictable at same average rate |
| Latency | Low, deterministic | Can spike; requires buffering |
| Required by | Broadcast (ATSC/DVB), some live encoders, streaming ladders | VOD, archival, most web delivery |
| Best for | Live broadcast, legacy multiplexers | On-demand, storage-efficient delivery |
Why broadcast still demands CBR
A broadcast multiplexer reserves a fixed slot per channel on the transport stream. VBR would overflow that slot, so CBR (or capped VBR) is a hard requirement. Same for some live encoder configurations where the uplink rate is fixed.
Why VOD should use VBR
On-demand has no slot constraint — only a file to serve. VBR lets a 4 Mbps average look like 6 Mbps when it matters (action, panning) and 2 Mbps when it does not (talking heads). That is pure quality for free, which is why every streaming ladder uses VBR rungs.
Two-pass is the pro move
FAQ
Common questions
Is CBR ever better quality?
No — for the same average rate, VBR is always at least as good, and usually visibly better. CBR wins only where the delivery channel requires a flat rate.
What bitrate mode do streaming platforms use?
ABR ladders are built from VBR rungs (or capped VBR for live). The player then adapts between rungs based on bandwidth.
Does the API support both?
Yes — CBR for live/broadcast outputs, two-pass VBR for VOD, configurable per job.
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