Beat sync — flash or zoom on every beat

There's no tempo-tracking or AI model here, the same way Green Screen keys a colour instead of segmenting with a model and Auto-Reframe tracks motion instead of running a face detector: a real beat-tracking model is tens of megabytes and needs real compute, which breaks the "free, no upload, runs entirely client-side" promise every tool on this site keeps. This uses spectral-flux onset detection instead — classic, decades-old signal processing that compares the audio's full spectrum from one short frame to the next, and flags a beat wherever a lot of frequency bins suddenly get louder at once, the signature of a kick, snare, or clap. Peaks that clear an adaptive threshold and sit at least a short minimum distance apart are the detected beats.

Flash lays a quick white overlay on the frame right after a detected beat, fading out in well under a second. Zoom Punch scales the picture up for an instant and eases back down the same way. Both are timed from the nearest beat before each frame, and both decay fast enough to read as a hit rather than a sustained change — use either one alone, or both together, and set how strong with Intensity.

Sensitivity controls how much a moment in the audio has to stand out to count as a beat: Low only catches the clearest, sharpest hits, High catches more, including softer ones. Because this can find more beats than you want an effect on, "Land the effect on" can skip ahead — every 2nd or every 4th detected beat instead of every one — without changing which moments were actually detected.

The video is genuinely re-encoded, because flashing or zooming means drawing new pixels on every frame — there is no wrapper trick for that. The audio itself is never modified, only analysed to find the beats, so it's copied across as compressed packets exactly like the site's other video tools do, provided it's AAC. Anything else would need a decoder and an encoder this tool doesn't carry, so it's dropped rather than silently guessed at, and the plan says so before you convert anything.

Listening for beats, decoding, drawing the effect and video encoding all happen in this page. There is no server here to send the video to, and the page's security policy blocks any connection to anywhere but this site. Here is how that is enforced.