How exact-size compression works
File size is simply bitrate × duration. To hit 10 MB, CompressLab subtracts the audio and container overhead from your target, spreads the rest across the length of the video and encodes at a constant bitrate. After encoding it checks the real size and, if the encoder overshot, re-encodes once with a corrected bitrate. Targets are hit within a few percent.
How small can a video get?
There is a floor: browsers’ encoders won’t go below roughly 24 kbit/s of video. For a 4-minute video that means about 0.9 MB minimum — and at that size you get 144p at 10 frames per second. The slider never goes below what’s possible for your videos and tells you the minimum with and without sound.
Batch: many videos, one limit
With several videos, the slider sets the size of the longest one. All videos share the same bitrate, so they all look equally good and none is over the limit. Need a different size for one video? Turn on Advanced settings and press ⚙ next to it.
Common targets
- 8 MB, 10 MB — Discord, GitHub issues
- 18 MB — fits a 25 MB email attachment (attachments grow by about a third when sent)
- 2, 8, 32, 64 MB — typical upload limits on WordPress, Moodle and other sites
- 1 MB — picture messages (MMS)
10 MB: what quality to expect
| Video length | Recommended resolution | Video bitrate |
|---|---|---|
| 15 s | 1080p | ≈ 4.8 Mbit/s |
| 30 s | 1080p / 720p | ≈ 2.4 Mbit/s |
| 1 min | 720p | ≈ 1.2 Mbit/s |
| 2 min | 540p | ≈ 0.55 Mbit/s |
| 5 min | 360p | ≈ 0.2 Mbit/s |
The numbers assume normal stereo sound (96–128 kbit/s); CompressLab automatically lowers the audio bitrate for long videos so the picture gets more of the budget.
Tips for the best result at a small size
- Trim first. Cutting a 60-second clip to the 25 seconds that matter more than doubles the quality.
- Lower the frame rate. 60 fps game footage at 30 fps looks nearly the same and gets twice the bits per frame.
- Let resolution go down. A clean 720p beats a blocky 1080p. Set Resolution to “Auto”.
- Use HEVC or AV1 only if the recipient can play it. They are 35–45% more efficient, but many apps and older devices can’t play them. H.264 is the safe default.
Questions
Why is my 10 MB file 9.5 MB?
A small safety margin guarantees it stays under the limit even if a site counts megabytes slightly differently.
Can I keep the original resolution?
Yes — that is the default. The slider then only lowers the bitrate. Choose “Auto” if you want the resolution lowered when the size is small.
Does it work for long videos?
Yes, there is no length or file size limit. For very small targets you can also split the video into parts.
How do I make a video exactly 10 MB?
Set the slider to 10 MB. CompressLab calculates the bitrate from the length, encodes, checks the result and re-encodes once if needed, so it lands just under 10 MB.
Last updated: 2026-10-30