Free tool
A/V sync test
Check lip sync through a screen, projector, LED wall or stream. The picture flashes, the pendulum (or metronome) passes center and the ball hits the floor on the same frame as a 1 kHz beep, once a second. If they don’t land together at the far end, something in the chain is adding delay.
30 seconds, loops cleanly. H.264 and AAC 48 kHz, so it plays on media servers, switchers, Resolume, PowerPoint and phones. In the file itself the beep and flash line up to within 1 ms.
Find your offset
Play this through the system you are checking, then drag the slider until the flash and the beep happen at the same moment where you are standing. The number is how much delay to add to the audio (or the video, if it reads negative).
At 0 ms the beep and flash leave this device together.
Bluetooth speakers and headphones add their own delay, so use a wired output for this.
Reading the result
- Beep before the flash: audio is ahead of the picture. This is the usual case, because screens, scalers and LED processors add a few frames. Delay the audio at the console or DSP by that amount.
- Beep after the flash: audio is behind. Look for delay on the audio path (a wireless system, a DSP with alignment delay, or a stream encoder) or delay the video.
- One frame is about 33 ms at 30 fps and 17 ms at 60 fps. Most people notice audio leading by more than 45 ms, or lagging by more than about 125 ms.
- Sound takes about 1 ms per foot to travel, so stand where the audience will be. 30 feet from the speakers adds about 27 ms of audio lag on its own.