How to Make a Video File Smaller Without Ruining It
Short answer
Resolution is the biggest lever: dropping 4K to 1080p cuts the file to roughly a quarter before anything else changes. After that, CRF controls quality directly — 23 is a good default, and each increase of about 6 halves the size again.
Published · Checked
Resolution first
Halving both dimensions quarters the pixel count, and file size follows roughly in step. Going from 3840×2160 to 1920×1080 is the single most effective change you can make.
The question worth asking is where the video will actually be watched. On a phone screen, the difference between 4K and 1080p is imperceptible. Even on a laptop it is marginal for most content.
Then CRF, not bitrate
CRF stands for Constant Rate Factor. Rather than forcing a fixed bitrate, it targets a consistent visual quality and spends bits where they are needed — more on complex motion, fewer on static scenes.
Lower numbers mean higher quality. 18 is effectively visually lossless, 23 is a sensible default that most people cannot fault, and 28 starts to look soft on detailed footage. Each step of roughly 6 halves or doubles the file size.
Setting a fixed bitrate instead is worth doing only when you have a hard size target to hit, such as an upload limit.
| CRF | Quality | Use for |
|---|---|---|
| 18 | Visually lossless | Archiving, further editing |
| 23 | Very good | General sharing — a sensible default |
| 28 | Noticeably softer | When size matters more than detail |
| 32+ | Visibly degraded | Previews and thumbnails only |
Encoder speed trades time for size
The encoder preset controls how hard the compressor works. A slower preset finds better ways to represent the same picture, producing a smaller file at identical quality — but it can take several times longer.
In a browser, where encoding is already slower than native software, 'very fast' is usually the right compromise. For a file you will distribute widely, the extra wait for a slower preset may be worth it.
- Lower the resolution first — it is the biggest single win
- Use CRF 23 unless you have a specific reason not to
- Check the audio bitrate: 320 kbps on a screen recording is wasted
- H.264 MP4 for compatibility; VP9 WebM if it is for your own website