BRAW Constant Bitrate and Constant Quality solve different production problems. Constant Bitrate makes data consumption easier to predict. Constant Quality lets the encoder vary the data rate so complex frames can receive more information. The choice is not “fixed quality versus variable quality.” It is a decision about which constraint the production wants to hold more tightly.
If the hard constraint is card time, offload cadence, or storage budget, Constant Bitrate is easier to plan. If the hard constraint is maintaining a quality target across scenes of changing complexity, Constant Quality is designed for that behavior.
How Constant Bitrate behaves
BRAW Constant Bitrate uses ratio labels: 3:1, 5:1, 8:1, and 12:1. At a fixed resolution and frame rate, each option targets a predictable stream. Lower ratios record more data; higher ratios record less.
This predictability helps with:
- Scheduling card changes during interviews or events
- Knowing whether the card pool can cover a shooting block
- Estimating daily source, backup, and archive capacity
- Planning offload stations and copy windows
- Keeping multi-camera data within a fixed budget
“Constant” does not mean every finished file will match a calculator to the byte. Audio, metadata, file splitting, formatting, and implementation overhead still exist. It means the codec strategy is built around a defined bitrate family rather than allowing scene complexity to drive an open range.
How Constant Quality behaves
Constant Quality uses Q0, Q1, Q3, and Q5 labels. Q0 applies the least quantization and targets the highest quality in the family. Q5 uses more moderate quantization for better efficiency.
The encoder can spend more data on frames that are difficult to compress and less on frames that are simple. A locked-off subject against a smooth wall may use less data than handheld foliage in rain at a high ISO. This is valuable when the production would rather let file size change than let a difficult frame be squeezed into a fixed target.
The operational consequence is a range:
- Total storage cannot be predicted as tightly.
- Maximum write speed matters more than the average.
- Card record time may change from scene to scene.
- A “normal” test can underestimate a difficult location.
For this reason, BRAW Planner displays a minimum-to-maximum estimate for Q modes and uses the upper value to suggest a drive target.
Why Q0 is not simply “better than 3:1”
Q0 and 3:1 are based on different rules. Q0 tries to protect a quantization target and can move across a wide bitrate range. 3:1 targets a predictable compression relationship. Their data rates can overlap, and Q0 can exceed a 3:1-like rate in a very complex scene.
A comparison should ask:
- Does the scene contain fine, random, moving texture?
- Is the exposure clean, or will noise increase complexity?
- Does the shot require keying, VFX extraction, or aggressive grading?
- Is the recording medium approved for the possible peak?
- Can the production tolerate a shorter-than-expected card time?
If the last two answers are no, the theoretical quality benefit is irrelevant because the workflow cannot safely support it.
Why Q5 is not simply “the same as 12:1”
Q5 is the most storage-efficient Constant Quality setting, but it still reacts to the frame. In a simple scene, it may produce very low data use. In a complex scene, it can rise toward the territory of less-compressed Constant Bitrate modes.
12:1 takes the opposite approach: it gives the crew a more predictable storage rate at the highest common Constant Bitrate compression. A production choosing between them is choosing between adaptive data use and predictable data use, not merely between two small-file settings.
Decision matrix
| Production condition | Better starting family | Why |
|---|---|---|
| Fixed card pool and long continuous rolls | Constant Bitrate | Predictable duration is easier to schedule |
| Highly variable texture with image quality prioritized | Constant Quality | Encoder can spend more data on difficult frames |
| Remote location with limited backup capacity | Constant Bitrate | Daily volume is easier to guarantee |
| VFX plates with approved fast media | Constant Quality or low-ratio CBR | More room for difficult detail; test both |
| Multi-camera event | Constant Bitrate | Aggregate storage and offload are easier to model |
| Controlled studio interview | Either | Simple images may work efficiently; test for the delivery |
| Uncontrolled documentary environments | Depends on the limiting risk | CQ protects variable scenes; CBR protects scarce media |
This is a starting matrix, not a substitute for tests. The same project may use different settings for different units or scene types if the handoff records those changes clearly.
Storage planning example
Suppose a single camera records 6K at 24 fps for three hours. A fixed 5:1 estimate can be calculated as one working number, then expanded with a 20% safety margin. A Q1 estimate should remain a range. The media pool must cover the high side if a complex scene can occur, while the production manager may use the midpoint only for a rough budget scenario.
For write speed, use the high side. For best-case record time, the low side can be informative, but it should not become the schedule promise. A card plan based on the most optimistic Q result can force media changes during the one moment that cannot be repeated.
Test for complexity, not convenience
A useful Constant Quality test contains the material most likely to raise the bitrate:
- Dense leaves, grass, gravel, hair, fabric, water, smoke, or confetti
- Handheld or rapid camera movement
- High shutter detail
- Underexposure or high-gain noise
- Fast subject motion across detailed backgrounds
- Lighting effects that change texture frame by frame
Record long enough to observe sustained behavior, not a five-second clip. Fill enough of the medium to expose thermal or cache-related slowdowns. Then inspect the footage in the intended grade and compare the actual data rate with the planned range.
A reliable choice in three questions
- Which failure hurts more: variable file size or constrained image detail? If missing a continuous roll is unacceptable, predictability may win. If the shot is controlled and irreplaceable detail is the priority, adaptive bitrate may win.
- Can the entire path support the maximum? Include the recording medium, cable, offload reader, workstation storage, backup target, and archive.
- Did the real scene pass a real test? Menu labels cannot replace footage.
Use the BRAW calculator to compare both families with the same resolution, frame rate, capacity, duration, and buffer. Keep Constant Quality as a range. That one interface difference reflects the most important operational difference between the modes.
Sources and calculation notes
- Blackmagic Pocket Cinema Camera technical specifications: camera-specific formats and storage-rate reference tables.
- Blackmagic RAW overview: manufacturer information about the codec and encoding modes.
- BRAW Planner methodology: the estimation formulas, unit conventions and limitations used on this site.
Workflow suggestions in this guide are planning guidance, not a claim that a particular camera or drive has been tested by the author.
Use the BRAW storage and recording-time calculator to model your exact resolution, frame rate, compression setting, safety buffer, and media capacity.