How video compression works
What the settings do, and how a target size is reached.
A video's size is its bitrate multiplied by its length. Compression lowers the bitrate by encoding the picture more efficiently, by keeping fewer pixels, and by using a lighter audio track. Video Compressor re-encodes to H.264 (the most widely playable video format) with AAC audio in an MP4 file.
Settings
| Quality presets | Constant-quality encoding (CRF) 21 / 24 / 28 for High / Balanced / Smaller. Lower CRF = more detail, larger file. |
|---|---|
| Manual CRF | Advanced: any value from 18 to 35. |
| Resolution | Shorter side capped at 1080, 720 or 480 pixels; never upscaled. |
| Audio | AAC 128 kbps, AAC 64 kbps, or removed. Stereo. |
| Encoding speed | Faster / Balanced / Slower presets; slower gives smaller files at the same quality. |
| Older devices | H.264 Main profile, level 4.0, max 30 fps. |
Target size
With a target, the encoder works out a bitrate: target bits × 0.96 headroom ÷ duration, minus the audio bitrate. If the first encode overshoots, it encodes once more with the bitrate scaled by the measured overshoot. If the file still doesn't fit, you get the smaller result marked Above target. We warn you in advance when the bitrate is low for the chosen resolution.
Checks before download
- The output must contain a valid H.264 video stream, and audio if you kept it.
- Its duration must match the original within 1 second or 1%, whichever is larger.
- Rotation is applied to the picture so portrait videos display upright everywhere; metadata such as location is removed.
- If an MP4 re-encode would be larger than your original, you get the original back.