What does a clapperboard actually do?
It marks the start of a take for the picture and the sound at once. The visible clap and the audible crack happen together, so an editor can line up the camera and the sound recorder exactly.
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A digital clapperboard for your phone
Hold the phone up to the cameras and press Clap. The screen flashes white and cracks at the same moment, giving every recording one sharp mark to line up by.
A digital clapperboard does the job of the striped wooden slate: it makes one moment that every camera sees and every microphone hears, so the recordings can be lined up afterwards. Open this page on a phone, fill in the scene and take, hold it up in shot and press Clap: the sticks snap shut, the whole screen flashes white and a sharp crack plays in the same instant.
That flash and crack give editing software, and the tools on this site, a clean spike in the sound and a frame you can point to in the picture. It works with any camera and any recorder, needs no timecode box and costs nothing. Scene, roll and take stay in your phone’s browser; nothing you type is sent anywhere.
Once you have filmed, drop the files into sync multiple cameras or, for one camera and a recorder, sync external audio. They match on the crack in seconds.
How to use the digital clapperboard
Fill in the slate
Type the Production, Roll, Scene and Take, and pick the Timecode frame rate (24, 25 or 30 fps) for the running clock.
Go full screen and turn the volume up
Press Full screen (F) so the slate fills the phone, and raise the phone’s volume so the crack is loud on every microphone. On an iPhone, Safari keeps the page view instead of full screen.
Clap in front of the cameras
With every camera and recorder rolling, hold the phone in shot and press Clap (Space or K). Turn on Count down to get three pips and the clap on the fourth.
Move on to the next take
With Next take after each clap on, the take number goes up by one after every clap, ready for the next slate.
Why a clap makes syncing easy
Lining up recordings means finding the same moment in each of them. Ordinary speech works, but it is soft-edged: the start of a word ramps up over a few milliseconds and a noisy room blurs it further. A clap is the opposite. It goes from silence to full volume almost instantly, so it shows as a tall, narrow spike in every waveform, and the frame where the sticks meet is easy to point at.
Automatic sync uses the same idea. With a crack at the start of each take, matching by sound has one unmistakable feature to lock on to, which is why the confidence goes up even in a busy location.
How the flash and the crack are kept together
Phones don’t play sound the instant they are asked to. The browser reports how long its sound output takes, and the clapperboard schedules the crack on the audio clock while drawing the flash on the matching screen frame, so the two leave the phone together as closely as the device allows. A phone connected to Bluetooth headphones or a speaker adds that link’s delay, so play the crack through the phone’s own speaker.
Getting the most from it
- Hold the screen square to each camera and close enough to fill a good part of the frame. Light from behind the cameras can wash the flash out.
- Clap once per take, near the start. On long events, a second clap at the end makes drift easy to measure.
- If a camera is far away, its microphone hears the crack a little late, about 3 ms for every metre. Matching by waveform to the nearest recorder avoids that.
- The page uses a screen wake lock where the browser supports it, so the phone doesn’t dim between takes.
Digital slate or a real clapperboard?
A wooden or acrylic clapperboard needs no battery, is readable from across a set and is what crews expect to see. A phone slate is always in your pocket, adds a flash that shows even when the sticks are out of focus, and can count takes for you. For vlogs, interviews, weddings and music videos shot on phones and mirrorless cameras, the phone does everything the sync needs.
If the footage then needs fixing within a single file, rather than lining up separate files, the clap helps there too: fix the audio sync can jump straight to it.
Questions about the digital clapperboard
Is a phone accurate enough as a slate?
Yes for syncing. The crack is scheduled on the phone’s audio clock using the output delay the browser reports, and the flash is drawn on the matching frame. Use the phone’s own speaker, not Bluetooth, so no extra delay creeps in.
Do I need to install an app?
No. The clapperboard runs in the phone’s browser. Add the page to your home screen if you want it one tap away on set.
Is the scene and take information sent anywhere?
No. What you type stays in this browser on your phone so it is there next time, and it isn’t included in analytics.
Why doesn’t full screen work on my iPhone?
Safari on iPhone doesn’t let web pages go full screen, so the slate stays inside the page. Turn the phone sideways for a larger slate.
Can I sync the clips without a clap?
Usually, yes: matching by sound works on speech too. The clap simply makes it faster and more certain, especially in noisy places.