Enter a file-size budget and duration to find the average video bitrate available after audio. Use decimal MB, where one MB is 1,000,000 bytes. If a service uses MiB instead, convert its limit before entering it. The result is an average-rate budget; it does not set an encoder’s quality mode or maximum bitrate.
How the calculation works
Available video Mbps = target MB × 8 ÷ seconds ÷ (1 + allowance / 100) − audio kbps ÷ 1,000. The allowance is an editable assumption for container and metadata bytes. Zero means those bytes are ignored. Audio is the combined bitrate of every exported audio stream.
Worked example
A 100 MB budget for 60 seconds with 320 kbps audio and no allowance leaves about 13.013 Mbps for video. With a 3% allowance, it leaves about 12.625 Mbps. These are planning targets, not promises that a variable-bitrate encoder will hit the exact size.
Before using the result
Choose a margin below a strict upload limit, inspect the finished file size and adjust the export if necessary. Negative remaining video budgets are rejected: the chosen audio already needs more space than the target permits. Multiple audio tracks, thumbnails and large metadata can change the overhead. A peak VBR value is not an average.
Keep the source values with your project notes. A number calculated from an assumed bitrate or representative sample is only as useful as that assumption. Check a real file or measured export when a deadline, upload cap or storage purchase depends on the answer.