How Large Will a Compressed Video Be? Estimate from Bitrate and Duration
Video file size is driven primarily by duration and encoded average total bitrate. Resolution influences how much bitrate looks acceptable, but it cannot predict final megabytes by itself.
The basic estimate
At 4 Mbps total average bitrate for 120 seconds, rough data is 4 × 120 ÷ 8 = 60 MB, plus small container overhead. Keep units consistent: Mbps and MB/s differ by a factor of eight.
- Add video and audio bitrate.
- Use actual duration in seconds.
- Treat the result as capacity planning.
Why CRF cannot promise a fixed size
CRF asks the encoder for broadly consistent visual quality. A static lecture and fast action at the same CRF use different average bitrates, so identical duration and resolution can still produce different bytes.
Resolution, frame rate, and complexity
More pixels, higher frame rate, noise, rain, foliage, and rapid motion usually demand more data for similar quality. Lowering resolution often reduces the demand, but not by a fixed ratio.
Plan more reliably with tinyclip
Encode a representative segment at the target CRF and resolution, calculate output bytes per minute, and extrapolate with headroom. The full output remains the final measurement.
References
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