Five contributors to file size
| Factor | Meaning | When reduced |
|---|---|---|
| Duration | How long the streams run | Removing unused time directly cuts content |
| Resolution | Pixels in every frame | Less detail and processing |
| FPS | Frames stored per second | Motion may look less smooth |
| Quality / bitrate | Data used over time | More compression artifacts may appear |
| Audio | The sound stream | Muting removes the audio component |
Resolution sets pixels per frame
4K, FHD and HD describe frame dimensions. More pixels usually give an encoder more visual information to handle.
A small player may not need the full source resolution. Create a delivery copy while keeping the master for editing or enlargement.
FPS divides each second into frames
30fps represents about 30 frames per second and 60fps about 60. Fast action may benefit from a higher rate; a static presentation may not.
60fps is not guaranteed to be exactly twice the file size of 30fps because frame similarity, codec and quality also matter.
Quality and bitrate describe data over time
Bitrate is the amount of data assigned to video and audio over a period. More data can preserve detail but tends to create a larger file.
Quality presets group encoder settings into understandable choices. Inspect text, hair, foliage and fast motion because they expose compression early.
Estimate the size of a one-minute video
Approximate file size in MB is (video bitrate + audio bitrate) × duration in seconds ÷ 8. The examples below use decimal MB, where 1 MB is 1,000,000 bytes.
These estimates assume fixed bitrates. Variable bitrate, codec efficiency and container overhead can make the downloaded file differ.
| Use | Before | After | Estimated size |
|---|---|---|---|
| Moderate-motion FHD | 1080p · 60fps · 12 Mbps video + 128 kbps audio | 1080p · 30fps · 6 Mbps video + 128 kbps audio | About 91.0 MB → 46.0 MB (about 49.5% less) |
| Messenger or web sharing | 1080p · 30fps · 8 Mbps video + 128 kbps audio | 720p · 30fps · 3 Mbps video + 128 kbps audio | About 61.0 MB → 23.5 MB (about 61.5% less) |
| Social copy from a 4K master | 4K · 60fps · 20 Mbps video + 192 kbps audio | 1080p · 30fps · 6 Mbps video + 128 kbps audio | About 151.4 MB → 46.0 MB (about 69.7% less) |
MP4 is not a quality level
MP4 and WebM are containers; H.264 and VP9 are codecs that encode the video stream. Two MP4 files can use different settings and therefore have different quality and size.
Only My Kit currently outputs MP4/H.264 or WebM/VP9, with source, 24, 30 or 60fps and audio keep or mute. Video Compress provides High, Balanced and Smaller file presets.
Audio and unused time count too
A video can include a separate audio stream. Muting is reasonable for a silent screen capture, but not when speech carries the meaning.
Trimming unneeded opening and ending time reduces frames and audio without lowering the quality of the remaining segment.
A strategy for each destination
| Destination | Check first | Protect |
|---|---|---|
| Messenger | Unused time, resolution, quality | Readable text |
| Duration and resolution | Attachment limits vary | |
| Web | Rendered resolution, format, quality | Loading experience |
| Social | Range, ratio, resolution | Platform rules can change |
| Archive | Usually keep the master | Separate master and delivery copy |
Compare one change at a time
Trim first, adjust excessive resolution next, then compare FPS and quality. This order makes the cause of each visual change easier to see.
Only My Kit separates Video Resize, Compress and Convert. Processing runs in the browser, although large and 4K sources can be limited by mobile memory and heat.
FAQ
- Does 60fps to 30fps halve the file?
- Not reliably. Codec, scene changes, quality and audio also determine size.
- Does MP4 always make a video smaller?
- No. MP4 is a container; codec and encoding settings determine the output.
- Resolution or quality first?
- If the source greatly exceeds the destination size, set a useful resolution first and then inspect quality.