&mirror

Inverts the video so it is the mirror reflection

General Option! (&push, &room, &view, &scene)

Options

Example: &mirror=2

Value	Description
(no value given)	Mirroring is forced for all videos
0	Preview video is mirrored only (excluding rear cameras and OBS Virtualcam/NDI)
1	Mirroring is forced for all videos
2	Inverts the default; local previews are not mirrored, but guests are mirrored
3	Same as default, except everything is mirrored, including text - useful for teleprompters

Details

Mirroring does not work if using the browser's native video full-screen button. Use &effects=2 instead for this use case.

Try F11 or the Electron Capture app (right-click → Resize window -> Fullscreen) to hide the browser menu instead.

Alternative method for mirroring and flipping

If you are looking for a form of rotation and flipping that rotates the actual video, rather than relying on CSS to achieve it, you can check out the sender-side &effects options. https://vdo.ninja/beta/?effects=-1, which will flip the video https://vdo.ninja/beta/?effects=-2, which will flip and mirror the video https://vdo.ninja/beta/?effects=2, which will mirror the video Effects however may increase CPU/GPU usage, and could cause frame rate instability, especially if the browser tab is not in active focus.

Dedicated teleprompter tool that works for most sites

There's a dedicated tool for mirror, flipping, and rotating websites as part of VDO.Ninja as well:

Teleprompter Tool

In case the built-in options to mirror or flip don't work, the teleprompter app might be a good alternative.

Related

Teleprompter Tool&effects&flip