A/B Testing Video Bitrate Formula
Learn how to estimate video file sizes, total delivery data, and data savings when comparing two bitrate variants.
This calculation estimates how a change in average video bitrate affects the video-only file size and the total data delivered across expected complete views. It helps quantify the delivery-data difference, while viewing quality and playback results still need to be tested separately.
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Estimated Delivery Data Difference
Where:
Find the per-view size difference from the two bitrates and video duration, then multiply it by the expected number of complete views. A positive result means Variant B uses less delivery data.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| bitrateA - Variant A bitrate | The average video bitrate for the baseline variant. | Mbps |
| bitrateB - Variant B bitrate | The average video bitrate for the comparison variant. | Mbps |
| videoDuration - Video duration | The length of one video asset. | minutes |
| expectedViews - Expected video views | The estimated number of complete video plays. | views |
Step-by-Step Calculation
Convert minutes to seconds
Bitrate is measured per second, so the video length must first be converted from minutes to seconds.
durationSeconds = videoDuration * 60
Estimate Variant A file size
Multiplying Mbps by seconds gives megabits; dividing by eight converts the result to estimated decimal megabytes.
fileSizeA = bitrateA * durationSeconds / 8
Estimate Variant B file size
Use the same process for Variant B so both file estimates use the same duration.
fileSizeB = bitrateB * durationSeconds / 8
Estimate total delivery for each variant
Multiply each per-view file size by complete views, then divide by 1,000 to convert decimal MB to decimal GB.
totalDeliveryA = fileSizeA * expectedViews / 1000; totalDeliveryB = fileSizeB * expectedViews / 1000
Calculate the delivery-data difference
A positive difference indicates that replacing A with B reduces estimated delivery data. A negative difference means B uses more.
deliveryDataDifference = totalDeliveryA - totalDeliveryB
Calculate bitrate reduction
This expresses Variant B's bitrate change relative to Variant A.
bitrateChangePercent = (bitrateA - bitrateB) / bitrateA * 100
Example: 10-minute video at 8 Mbps versus 5 Mbps
Convert duration
10 * 60
600 seconds
Estimate Variant A size
8 * 600 / 8
600 MB per video
Estimate Variant B size
5 * 600 / 8
375 MB per video
Estimate total delivery
600 * 100000 / 1000 and 375 * 100000 / 1000
60,000 GB for A; 37,500 GB for B
Find the difference
60000 - 37500
22,500 GB saved
Calculate bitrate reduction
(8 - 5) / 8 * 100
37.5%
Final Result
For 100,000 complete views, switching from 8 Mbps to 5 Mbps is estimated to reduce video-only delivery by 22,500 GB.
Assumptions
- ✓The entered bitrate is the average video bitrate for each complete video.
- ✓Each expected view is assumed to play the whole video once.
- ✓File and delivery estimates use decimal units, where 1 GB equals 1,000 MB.
- ✓The calculation covers video data only and keeps video duration unchanged between variants.
Limitations
- !Audio streams, subtitles, container overhead, manifests, and encryption overhead are excluded.
- !Adaptive streaming can deliver different renditions to different viewers.
- !Actual viewing duration can be lower than the full video duration.
- !Caching, retries, player behavior, devices, and protocols can change actual transferred data.
- !A delivery-data result does not measure visual quality, startup time, buffering, or audience response.
Common Mistakes to Avoid
Entering a bitrate in Kbps when the input expects Mbps.
Using impressions or page visits instead of expected complete video plays.
Treating MB and MiB, or GB and GiB, as identical units.
Comparing variants with different durations without accounting for the duration change.
Assuming a lower bitrate will preserve acceptable quality for high-motion or detailed footage.
Related Formulas
Frequently Asked Questions
How do you calculate video file size from bitrate?
Multiply average bitrate in Mbps by duration in seconds and divide by eight. The result is an estimated video-only size in decimal MB.
Why is the bitrate divided by eight?
Bitrate is measured in bits, while file size is usually expressed in bytes. Eight bits equal one byte.
What does a positive delivery-data difference mean?
It means Variant B is estimated to deliver less data than Variant A across the entered number of views.
Can the delivery-data difference be negative?
Yes. A negative result means Variant B has a higher bitrate and is estimated to use more delivery data than Variant A.
Does the formula include audio bitrate?
No. It uses the video bitrate values entered and excludes audio and other delivery overhead.
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