A tab only appears in the list once there's a video actually running in it. Four things get in the way.
On Google Drive, Vimeo and YouTube, a video will often sit there showing a still frame with a play button over the middle of it. The page looks finished and ready, but nothing has started.
Click play on both videos, wait a second, then open Reaction Sync.
Put both tabs side by side, and keep both videos playing and unmuted while you get them paired. A tab sitting behind another one with its video paused or muted may not be picked up.
Once they're paired, mute and pause whatever you like — this only matters while you're setting up.
Reaction Sync can only reach tabs that were opened after it was installed. The same applies after it updates, and Chrome installs extension updates on its own — so a tab that worked yesterday may need this today.
Refresh both tabs and click play again.
A search page, a browse page, or the description page for a film or episode won't appear in the list, even on a site we support. You need to be on the page where the video itself is playing.
After picking your tabs you choose one of two ways to begin.
Start from Beginning jumps both videos to the first sync point and plays from there. Use it when you're sitting down to watch the whole thing.
Continue from Current Source Time leaves the source where it is and brings the reaction to match. Use it if you're already part-way through, or if you paired late.
Either one. Play, pause or seek on the source or the reaction, and the other follows on its own.
You don't need to keep the extension open while you watch.
Linked is the normal state. It means the two videos are tied together — pause one and the other pauses, seek one and the other follows.
Turning it off breaks that tie and lets you move each video on its own. There's one reason to do it: you're lining two videos up by hand and want to scrub freely without the sync pulling them back together while you work.
Turn it back on when you're done.
That's the drift meter. It sits in the top right corner of the reaction video and shows how closely the two are tracking each other.
Green means they're in sync. Red means they've slipped apart.
If it goes red, pause and play again — that forces both videos to snap back together.
You can switch it off in the extension with the Drift Meter checkbox if you'd rather not see it.
Not with the player's own speed control. Syncing assumes both videos are playing at normal speed, so leave the source and the reaction at 1x.
If either one is set to 1.5x or 0.75x, the two will drift apart. Set both back to 1x if that happens.
There is one exception, and it's built into the extension rather than the player — see videos slowly drifting apart.
The session ends. The other tab shows “Sync Connection Lost” and playback stops being tied together.
This is deliberate. Refreshing or navigating replaces the video the extension was tracking, and carrying on against the wrong one would put you out of sync without telling you.
Start the two videos again and pair as normal. If you were using a sync script it's still there — nothing is lost but the session itself.
Open the extension and click End Session. The two videos go back to being independent, and both tabs carry on playing whatever they were playing.
Closing either tab ends the session too.
A saved record of how a particular reaction lines up with its source.
Without one, you pair two tabs and mark the moment they match. With one, that's already done — open the link, pick your two tabs, and you're watching.
You can make your own once you've paired something: save it as a file, or as a link you can send to someone.
Only if they've made one, so it's worth asking. A creator marks the sync points once, saves a link, and posts it alongside the reaction — after that, anyone who follows them can press play without setting anything up.
Open both videos in their own tabs and press play on each. Then open the extension, pick the two tabs, and choose Load from Link. Paste the link, and it starts.
If you were sent a .sync file instead, use Load .sync File & Start and pick it from your computer. Same result.
Either way the alignment comes from the script — there's nothing for you to mark.
Pair the two tabs, then click Edit Script in the extension to open the timeline.
Before you start scrubbing, turn Linked off. While it's on, the sync engine keeps pulling the two back together, which fights you as you try to align them by hand. With it off, you can move each video freely.
Find a moment that appears in both, add a sync point there, and turn Linked back on to check it. When you're happy, save the script as a file or share it as a link.
Most reactions need only the first one. The others handle stretches where the two videos aren't running together.
The two line up here and play together from this point on. This is the normal one.
Freezes the source while the reaction keeps playing. Use it where the reactor pauses to talk about something.
The opposite — the reaction waits while the source plays on. Use it where the reactor skips ahead or watches a stretch without commenting.
Stops the session where the reaction finishes. Worth adding: without it, the site's own autoplay can start the next episode and carry the session off with it.
If they start together and get steadily further apart — rather than jumping out of sync at one moment — the two copies are almost certainly running at slightly different frame rates. A television cut at 25fps against a cinema cut at 24fps will separate a little more every minute.
In Edit mode, use the Videos playing at different speeds? dropdown to apply a correction. It adjusts the reaction's speed by a small amount to match, and it's saved with the script so anyone using it gets the same correction.
Click your profile picture in the extension and choose My Shared Scripts. Everything you've uploaded is listed there, with its link.
The full list is on the homepage, kept up to date as we add more.
You watch on your own subscriptions. Reaction Sync doesn't host, provide, or unlock any content.
Not on Prime Video — ads and the studio intros that vary by region are both handled.
On the other sites, ads aren't handled yet. We're working on it, but until then you'll want an ad-free plan.
30 days from the day you sign in with Google. No card, and nothing held back — you get the whole product.
After that you'll need a paid subscription to carry on. Current rates are on the pricing page.
We're still finding our feet on pricing, so if you're a reaction creator, or you've been using this and have thoughts on it, write to support@reactionsync.com. We're extending trials case by case for people willing to tell us what's working and what isn't.
In your browser, open the Reaction Sync extension, click your profile picture in the top right, and choose Manage Subscription. Your account page opens, with a Cancel subscription button on it. That's all — you don't need to contact us.
Future charges stop straight away, and you keep access until the end of the period you've already paid for.
Details in the refund policy.
Something not covered here? Email support@reactionsync.com and mention which two sites you were pairing.