mirror mode flips your script so it reads correctly in the reflection on a beam-splitter rig. without it, the glass shows your words backwards. with it, the reflected text reads normally while you look down the lens. that's the whole job, and it's why every teleprompter app has some version of it.
here's what it's actually doing, and how to pick the right flip.
why a beam splitter reverses your text#
a beam-splitter rig puts a piece of 45-degree glass in front of your camera. your phone lies flat under the glass, screen up. the glass reflects that screen back at you so you can read while looking straight down the lens.
a reflection reverses left and right. so the text on the phone comes back to you mirror-image, like words held up to a bathroom mirror. unreadable, basically.
mirror mode fixes this by pre-flipping the text. you reverse it on the screen first, the glass reverses it back, and the two cancel out. what you read in the reflection is the right way round.
if you're not using a beam splitter, you don't need any of this. reading straight off the phone needs no flip at all.
horizontal, vertical, both, or off#
open prompter cycles the mirror with one chip. it goes off, then horizontal, then vertical, then both, then back to off.
most people only ever touch horizontal. that's the standard beam-splitter flip, the left-right reverse that cancels the glass. set it once and the reflection reads normally for the rest of the shoot.
the reason there's more than one axis is that not every rig bounces the image the same way. a basic splitter does one bounce and reverses left-right. but a periscope rig adds a second mirror to fold the optical path, and that extra bounce can flip the image top-to-bottom instead. mount the phone upside down to clear a cable or a clamp and you've changed the geometry again.
so a single horizontal flip isn't always enough. open prompter does horizontal AND vertical independently, so you can match whatever your rig is doing instead of being stuck with one flip and a backwards script.
- horizontal. reverses left and right. the standard beam-splitter flip. start here.
- vertical. reverses top and bottom. for rigs that bounce the image upside down.
- both. flips both axes at once. for periscope setups, double-bounce rigs, or a phone mounted upside down.
- off. no flip. for reading straight off the phone with no glass in the path.
a simple way to choose#
you don't need to understand the optics. you need the reflection to read normally. so the decision is short.
not using a beam splitter? leave mirror off. you're reading right off the screen, nothing to cancel.
standard beam-splitter rig? set horizontal. this is the answer almost every time. one chip tap and the glass reads right.
odd geometry? if horizontal still looks wrong, your rig is bouncing the image a different way. try vertical. if that's still off, try both. one of the four states will land it. flip until the reflected text reads normally, then leave it alone.
there's no chart to memorize here. the chip cycles through all four states in a couple of taps, and your eyes tell you the moment it's right. set it during setup, not mid-take, and you'll never think about it again for that rig.
set it once and stop touching the phone#
mirror is a setup-time decision, not something you ride during a take. once the reflection reads right, the chip stays put for the whole shoot on that rig. break the rig down and rebuild it the same way tomorrow, and the same flip still works.
that pairs with how you run a beam-splitter rig. your hands belong on the camera, not on a phone buried under the glass. so you set the mirror, turn on focus mode to dim the chrome down to clean text, and drive everything else from a Bluetooth remote. mirror toggle is even one of the bindable remote actions, on the off chance you want to flip it without reaching in.
the point is that mirror disappears into the setup. you solve it once with your eyes, and then it's part of the rig like the clamp or the glass.
it's a baseline feature, not a paywall#
worth saying plainly. mirror mode in open prompter is on from day one, free, with no upgrade prompt.
the rest of the category doesn't treat it that way. plenty of teleprompter apps put mirror mode behind a subscription, as if flipping text left-to-right were a premium trick worth a monthly fee. it isn't. it's the one feature a beam-splitter user cannot work without, which is exactly why it gets paywalled.
open prompter is MIT-licensed and free, the whole feature set, no account and no subscription. mirror mode is part of that. so is two-axis support, which most paid apps don't even offer.
the full rig walkthrough#
mirror mode is one piece of running open prompter on a beam-splitter rig. the rest is going hands-free with a Bluetooth remote, routing a wired lavalier so voice tracking follows you from across the room, and turning on focus mode for clean glass.
the next step is the complete setup. the beam-splitter guide walks the whole rig from mounting the phone to standing back at your mark.