How do I blur faces in a protest video without putting people at risk?

Pixelate rather than blur, do it on your phone before the video goes anywhere, and treat the result as a reduction of risk, not a guarantee. Anonimo pixelates every face on the iPhone with no upload; pixelation is in the free tier. Then strip metadata and think about what else in the frame identifies people.

Pixelation over blur

A soft blur keeps the shape of a face, and a light one can be undone well enough to recognise someone who is already known. A coarse mosaic replaces the face with a handful of flat blocks and leaves far less. An emoji cover hides everything but looks out of place on serious footage; pixelation is the usual choice.

On the device

Put the phone in Airplane Mode if you want to be sure nothing syncs while you work.
Open the video in Anonimo, let it find the faces, and leave everyone covered. Choose pixelation.
Export. The pixelated copy is saved to Photos; the original stays. Decide what to do with the original before you turn the network back on.
Check the export for faces that turn away or appear in reflections and windows; a face the app never detected stays visible.

Metadata and everything else

A video file carries the time, often the location and the device model. Sharing through a messenger usually strips this; sending the file directly may not.
Signs, banners, tattoos, distinctive clothing, licence plates and the voices on the audio identify people as well as faces do.
The place itself, the time and who else appears can identify a small group even with every face covered.

If you want this done automatically on your iPhone, Anonimo finds every face in a video, groups them by person, and blurs everyone except the people you pick. Nothing leaves the phone.

Trade-offs

Coarser pixelation hides more and looks worse; for safety, coarser.
Covering everyone is safest and simplest. Keeping speakers visible means they have agreed to be seen.
No tool makes a video safe to publish. Blurring faces removes the most obvious identifier and nothing more.

Questions

Is blurring irreversible?

We do not claim that. Pixelation replaces the face with flat blocks and is far harder to undo than a light blur, but the original still exists until you delete it, and the rest of the frame can still identify people.

Can I pixelate faces without uploading the video?

Yes. Anonimo does everything on the iPhone, works in Airplane Mode and has no upload code.

Should I blur the police too?

That depends on where you are and why you are publishing; our country pages on filming people link the rules. Technically Anonimo treats every face the same, so you decide per person.