Video compression
Compress mode is for “this file is too big to send or upload.” It is not a converter. Input can be MP4, MOV, MKV, AVI, or WebM. Output is always MP4 with H.264 video and AAC audio (unless you strip audio).
The Windows app and the browser tool share the same two modes and the same CRF map. The app uses bundled FFmpeg; the browser uses ffmpeg.wasm and a 100MB ceiling because a tab will run out of memory on camera originals.
Quality presets
| UI label | x264 CRF | Use when |
|---|---|---|
| Low / small file | 28 | Chat apps, rough drafts, storage cleanup |
| Balanced (default) | 23 | Most sharing. The usual starting point |
| High | 18 | You still want a smaller file than the camera export, but it should look close to the source on a phone or laptop |
Lower CRF = larger file and more retained detail. Always start from the camera or editor export, not from a file you already uploaded to Instagram or WhatsApp. A second lossy pass cannot recover what the first pass threw away.
Target file size
Use this when the limit is a number: Discord 10MB, email 25MB, a form that rejects anything over 50MB. Shrynk probes duration with FFprobe, reserves ~128 kbps for AAC, and sets a video bitrate so the finished MP4 lands under the slider. If the clip is long, the picture has to get softer — that is the length × resolution × size trade-off, not a hidden setting.
If the source is already smaller than the target, you do not gain anything by “compressing up.” Send the original.
Remove audio
Screen recordings and silent B-roll often waste a third of the file on a mute track. Strip audio when the viewer does not need it. Target-size mode then spends the whole budget on the picture.
Free cap and Pro
- Free: one file, up to 100MB, unlimited times. Same rule in the browser and in the desktop app.
- Pro ($9 one-time): no 100MB cap, and batch compress a folder.
A 4K phone clip is usually over 100MB. That is the intended upgrade moment, not a tease — a browser tab cannot hold that encode reliably anyway.
Compress vs convert
| Compress | Convert | |
|---|---|---|
| Goal | Smaller, same kind of file | Different container or codec family |
| Output | MP4 only | Whatever pair you picked (including extract MP3) |
| iPhone MOV too big | Compress after you are fine staying in a movie file | MOV → MP4 if a device will not play MOV |
Need both (MOV → small MP4)? Convert first if playback is the problem; compress first if size is the problem and MP4 playback is already fine. Doing both blindly stacks generation loss.