BRAW recording time is the amount of usable media capacity divided by the recording data rate. The formula is easy; the reliable plan requires choosing a conservative data rate, reserving space, and accounting for the time needed to return media to camera.
Record time in seconds = usable capacity in GB × 1,000 ÷ data rate in MB/s
If a 1,000GB drive has 800GB allocated after a 20% reserve and the stream is 100MB/s, the estimate is 8,000 seconds, or about 2 hours 13 minutes. A Constant Quality mode needs a range because the bitrate can change with the image.
Advertised capacity is not a roll-time promise
Storage products are sold in decimal units. A 1TB drive contains one trillion bytes, which equals 1,000 decimal GB. Some operating systems display the same capacity as roughly 931GiB. That difference is a unit conversion.
Practical recording capacity can be lower for additional reasons:
- Filesystem and directory structures consume space.
- The device or camera may reserve capacity.
- A nearly full SSD may lose performance.
- Existing clips or test footage may still be present.
- The production may intentionally keep 10–30% unused.
This is why BRAW Planner asks for a reserved-capacity percentage in record-time mode. The reserve is not “lost.” It is operational headroom.
Calculate from the worst credible stream
Constant Bitrate modes produce the simplest estimate. Once the camera-specific MB/s rate is known, recording time is relatively predictable.
Constant Quality modes should be treated differently. Q0, Q1, Q3, and Q5 can use more data when the frame contains fine detail, noise, motion, or complex texture. Divide capacity by the maximum credible MB/s value to find the shortest credible record time. Divide by the low value for the best case. The actual clip may land between them or occasionally outside an average published range.
For an event schedule, use the short result. A card plan that works only when the scene compresses easily is not a plan.
Example: 512GB media at 4K DCI
Suppose a camera records 4K DCI, 24fps, BRAW 8:1. A general ratio-based estimate is approximately 42–43MB/s. Reserve 20% of a 512GB device:
- Usable planned capacity: 409.6GB
- Approximate time: 409,600MB ÷ 42.5MB/s
- Result: about 9,638 seconds, or roughly 2 hours 40 minutes
The exact camera table may differ, so use the manufacturer’s published rate for the specific format when available. The example shows the workflow: establish data rate, subtract reserve, divide, and round down for the schedule.
Do not schedule a media change at the exact calculated minute. Stop before the theoretical limit so the operator has time to react and the camera can close the clip safely.
Continuous roll versus recorded day
Two different questions are often combined:
- How long can one device record continuously? This matters for ceremonies, performances, interviews, conferences, and observational documentary scenes.
- How much media does the whole day require? This includes multiple cards, offload turnaround, camera count, and the percentage of the day actually recorded.
A card that holds 90 minutes may be sufficient for a narrative setup with short takes and regular resets. It may be unacceptable for a two-hour performance where a card change cannot be hidden. Plan around the longest uninterrupted block first, then around total recorded hours.
Build a media rotation, not only a capacity total
A three-card rotation can fail even when total capacity looks adequate. The offload station must copy, verify, and release a card before the other cards fill.
For each card, track:
- Expected roll time at the chosen setting
- Reader and source-media read speed
- Destination write speed under sustained load
- Copy time for the expected fill level
- Checksum verification time
- Time to label, log, and safely eject
- Travel time between camera and data station
If a 512GB card takes 50 minutes to copy and verify but the camera fills the next card in 35 minutes, the rotation will eventually stall. Adding cards can create a buffer, but faster verified destinations or a different recording setting may solve the real bottleneck.
Multi-camera recording time
Card duration per camera does not change merely because more cameras are recording. Aggregate media consumption does.
Three cameras, each using a 512GB card with a two-hour estimate, still receive about two hours per card. The data team, however, may receive three full cards in the same time window. The destination must absorb three times the volume, and the card pool must cover simultaneous turnover.
Staggering card changes can help continuity, but it does not reduce total data. Assign unique card IDs by camera and roll, and never depend on filenames alone to distinguish media.
High frame rate reduces real-world roll time quickly
At a fixed resolution and compression ratio, 60fps requires roughly 2.5 times the data of 24fps. A card that records 100 minutes at 24fps may record only around 40 minutes at 60fps.
When high-frame-rate footage is played back slowly, its timeline duration becomes longer, which can hide the acquisition cost. Storage is based on frames captured per real second, not seconds on the final timeline.
If a production alternates normal and high-speed capture, calculate each block separately. Do not average the frame rates unless the shooting ratio for each mode is known.
Use roll time to set on-set alerts
A simple operating procedure prevents a calculated limit from becoming a missed shot:
- Set a first warning at 70% of the planned usable time.
- Set a prepare-to-change warning at 85%.
- Treat the final reserved percentage as untouchable except for an emergency continuation.
- Log actual remaining time when a card is pulled.
- Compare actual duration with the estimate after the first card and revise the plan.
For Constant Quality, monitor capacity consumption during the most complex material. If the real rate is higher than the midpoint, update the rest of the day before the shortage appears.
Recording-time checklist
- Select the exact sensor window, recording fps, and BRAW setting.
- Obtain the camera-specific MB/s figure where possible.
- Enter the advertised decimal capacity in record-time mode.
- Reserve at least 10–20%; use more for uncertain or mission-critical work.
- Round the resulting time down for scheduling.
- Confirm one device covers the longest continuous event.
- Time a full copy and verification cycle.
- Check that the card rotation returns media faster than camera consumes it.
- Recalculate for high-speed shots and every additional camera.
Recording time is ultimately a system property. Capacity, data rate, device performance, crew process, and offload speed all have to remain in balance.
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.