What Is Video CRF? Balancing Quality, Size, and Time
CRF is a constant-quality control, not a target file size. The encoder spends more data on complex scenes and less on simple ones, so two videos at the same CRF can differ greatly in size.
CRF controls a quality target, not a megabyte target
Constant bitrate tries to spend a similar amount of data each second. CRF lets the encoder spend more on difficult scenes and less on easy scenes to keep visual quality more consistent. It fits the question “what quality can I accept?” better than “what exact size must I hit?”
Fast motion, particles, rain, foliage, noise, and fine texture produce larger files at a given CRF. A static presentation, flat background, or low-motion shot is easier to encode.
The actual tinyclip presets
| Preset | CRF | x264 preset | Audio bitrate |
|---|---|---|---|
| High quality | 18 | medium | 192 kbps |
| Balanced | 23 | faster | 128 kbps |
| Smallest | 30 | faster | 96 kbps |
CRF, resolution, and encoder preset
- Resolution: determines pixel count. Moving from 4K to 1080p often changes size more than a small CRF adjustment.
- CRF: controls how much loss blocks can tolerate. Too high produces blocking, banding, and missing texture.
- x264 preset: controls how much computation searches for an efficient representation. Slower usually saves bytes at similar quality but takes longer in a browser.
- Audio bitrate: becomes a larger share when pictures are simple or duration is long.
Find a CRF for your material
- Decide the final resolution first.
- Select a 30–60 second segment containing fast motion, shadows, and subtitles.
- Export at CRF 18, 23, and 30, or nearby custom values.
- Watch on the destination device and at the destination window size.
- Choose the highest CRF that still looks good enough, then encode the full video.
When an exact file-size ceiling is mandatory, one CRF pass is not the most predictable method. A professional desktop encoder with two-pass bitrate control is better suited to a strict limit.
References
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