ClappyBoardHow to sync audio and video with a clapperboard
The short answer
Find the first frame where the clapperboard's sticks touch, find the start of the clap's spike in your sound file, and line those two points up. Once they sit on top of each other, the whole take is in sync. You don't need timecode for this, just a clean clap at the start of every take.
Why picture and sound need syncing at all
Most indie shoots record sound twice. The camera records picture along with rough “scratch” audio from its built-in mic. A separate recorder captures the good sound from your boom or lav mics. This is called double-system sound: two machines, two sets of files.
The two machines start and stop at different moments. The recorder might start a few seconds before the camera, or keep going after it stops. Nothing inside the files tells your editing software how they fit together, so you have to show it.
Bigger productions often do this with timecode: a shared running clock fed into the camera and recorder. Plenty of shoots don't have that gear, and that's fine. A clap on every take does the same job by hand, and film crews have relied on it for nearly a century.
Why a clap lines up picture and sound
When the two sticks of a clapperboard slam together, two things happen at the same instant. The camera sees the sticks meet: there is one frame where they go from open to closed. The recorder hears a sharp crack, which shows up as a sudden spike in the waveform.
Line up that frame with that spike and every other moment in the take lines up too. It's a single reference point shared by two machines that otherwise know nothing about each other.
What the sync marks look like in your editor
You'll be hunting for these by stepping through frames and zooming into waveforms, so it helps to know what you're looking for.
| Slate | On the picture | On the sound |
|---|---|---|
| Clapperboard sticks | A few frames of the top stick falling, then the first frame where it touches the bottom stick. That's the mark. If the stick is a smear across two frames, use the first one where it clearly touches. | Low, fuzzy room tone, then a near-vertical spike, usually the tallest thing in the first few seconds. It dies away within a fraction of a second. |
| Flashing digital slate | The board looks normal, then the first frame that turns white. On some cameras that first frame is only partly white, a bright band across part of the picture. Count it as the mark: it's where the flash began. | A clap looks like the spike above. A beep looks like a solid block that starts abruptly and stays at one height until it stops. Mark its front edge. |
| Hand clap | Two hands coming together. Harder to pin down, because hands are soft and it's hard to see the exact frame they meet. | A spike, usually smaller and softer than sticks. |
How to sync the clap in your editing software
Every editing program names its buttons differently, but the steps are the same everywhere.
Bring in both files
Import the camera clip and the sound file for the same take. The scene and take called out on the slate, and your take log if you kept one, tell you which sound file goes with which clip.
Find the frame where the sticks meet
Play the clip up to the slate, then step forward one frame at a time. Stop on the first frame where the sticks are closed, or the first white frame of a flash. Add a marker there.
Find the start of the spike
Open the sound file and zoom in on the waveform around the clap. Put a marker at the very start of the spike, the moment it leaps up, not further along where it has already started to fade.
Line the two markers up
Slide the sound file along the timeline until its marker sits exactly under the picture marker. Most editing software can snap markers together, which makes this quick.
Check it by eye and ear
Play a moment where someone is talking, ideally on words with hard sounds like p, b and t. Lips should hit the words exactly. If it feels slightly early or late, nudge the sound one frame at a time until it looks right.
Link the clips and mute the camera's sound
Link or group the picture and the new sound so they stay together when you cut. Then mute or remove the camera's own rough audio so you only hear the good recording.
Check the end of long takes
On a long take, jump to the end and check sync again. Camera and recorder keep time separately and can slowly drift apart. If they have, a clap at the end gives you a second point to line up.
Slate mistakes that make syncing hard, and how they show up
Almost every sync headache in the edit starts with a slate that went slightly wrong on set. Here's what each one looks like when you get to the edit, and how to avoid it next time.
| On set | In the edit | Next time |
|---|---|---|
| Board held at the edge of frame or out of focus | You can't tell which frame the sticks close on | Ask the camera operator where to hold it before rolling |
| Board swung into frame as it clapped | The sticks are a blur across several frames | Hold still; move only the top stick |
| Clap from across the room | A small bump lost in echo and background noise | Clap close enough to the mic that it stands out |
| A timid tap instead of a clap | A spike no bigger than a word of dialogue | Make it crisp (soft sticks only for close-ups) |
| Clapped before the recorder was running | No spike at all in the sound file | Wait until both sound and camera say they're rolling |
| Someone talked or a door banged during the clap | Two spikes close together, and you're not sure which is the clap | Call “second sticks” and clap again |
| Scene and take not called out | You can't tell which sound file belongs to which clip | Say it toward the mic on every take |
For the full on-set routine, including soft sticks and second sticks, see how to slate a shot.
Tail slates: syncing from the end of a take
Sometimes you can't slate at the start. The shot might open on a very tight close-up, or a clap could break an actor's focus before an emotional scene. You can mark the end instead. That's a tail slate.
After the action, keep camera and sound rolling. The person slating brings the board in upside down, so everyone knows it's an end mark, calls “tail slate” with the scene and take, and claps. In the edit you sync it the same way; the mark is just near the end of the clip. Write tail slates in your log so the editor knows where to look.
Doesn't editing software sync on its own now?
Often, yes. Many editing programs can line up clips by comparing the camera's scratch audio with the recorder's sound and matching the shapes of the two waveforms. When it works, it saves a lot of clicking.
It needs something to compare, though. If the camera's audio is missing, very quiet, or full of wind or generator noise, automatic syncing can fail or land slightly in the wrong place. A sharp clap at the start of both recordings gives the software an easy match. And when it does fail, the clap is still there for you to sync by hand.
The slate also puts the scene and take on screen and in the sound file, so you can tell at a glance which pieces belong together. For what the rest of the board means, see what's written on a clapperboard.
Questions
Can I sync audio and video without timecode?
Yes. A clap on every take gives you one moment you can see and hear. Line up the frame where the sticks meet with the start of the spike in the sound, and the whole take is in sync.
Can I just clap my hands instead of using a clapperboard?
In a pinch, yes. Clap once, sharply, in frame and near the mic. It's harder to see the exact frame where hands meet than where sticks meet, and there's no scene and take on screen, so say them out loud first.
Where exactly do I put the marker on the waveform?
At the very start of the spike, the first moment the sound jumps up. The loudest point comes a little later and would put your sound slightly late.
Why does my sound drift out of sync during a long take?
The camera and the recorder each keep their own time, and the two can run at very slightly different speeds. Over several minutes that adds up. Check that the camera's frame rate and the recorder's settings match what your project expects, and use a clap at the end of long takes as a second sync point.
Does ClappyBoard send timecode to my camera?
No. ClappyBoard doesn't output timecode. It gives every take a sync mark, a white flash for picture and a clap for sound, which you line up by hand or let your editing software match.