Stream Audio Out of Sync With Video? Here's the Actual Fix

A message comes in during the stream: "is it just me, or is the sound off?" It's almost never just them. Lips not matching the words coming out of the speakers is one of the fastest ways to lose an online viewer, it reads as broken even when everything else about the stream looks fine, and the frustrating part is it usually has nothing to do with their internet connection and everything to do with one setting on your end that's never been touched.

Where the drift actually comes from

Video and audio don't take the same path through your gear, and that's the whole problem. Video gets scaled, compressed, and processed through more stages before it hits the stream, which takes a few extra milliseconds audio doesn't need. If your audio is coming from a separate source, a digital board's USB or Dante output routed into your encoder instead of straight off the camera mic, that path adds its own processing delay on top. The gear isn't broken, the two signals are just arriving at slightly different speeds, and a viewer's eye and ear are sensitive enough to notice even a small gap.

Diagnose it properly before you touch a setting

Don't judge sync from your encoder's local preview window, it can look perfectly synced there while the actual stream output is drifting, because the preview and the final encode aren't always processed identically. Watch the real, live stream on a second device instead, the same way a viewer would.

The clap test is the fastest way to measure it: record yourself clapping once on camera, on the actual stream, then scrub back through the recording and count how many frames separate the visual clap from the audio clap. That frame count tells you which direction to correct and roughly how far off you are.

Fixing it in OBS

Right-click the audio source in your Mixer panel and choose Advanced Audio Properties. There's a Sync Offset field for each source, measured in milliseconds. A positive number delays that audio source, a negative number moves it earlier. If your clap test showed audio arriving before video, add a positive offset in small steps, 50 to 100 milliseconds at a time, retest with another clap, and adjust until they line up.

Fixing it on an ATEM

If you're running a Blackmagic ATEM switcher, the delay usually needs to happen on the audio side to match video's natural processing lag. In ATEM Software Control, there's an Audio tab with a delay setting per input, adjustable in milliseconds. Same approach as OBS: small adjustments, retest with a clap, don't try to nail it in one guess.

The other common cause: buffer settings on a digital board's USB or Dante output

If your audio is routed from a digital mixing board into your encoder rather than a straight camera mic feed, check the board's USB or network audio buffer size, it's usually in the board's routing or I/O setup menu, not somewhere obvious. A larger buffer size reduces the risk of audio dropouts but adds processing delay, which is exactly the kind of tradeoff that quietly creates a sync problem nobody remembers making. Lowering the buffer size cuts the delay, but test for dropouts afterward, there's a real tradeoff here and the fix for one problem can reintroduce the other if you go too far.

Document the fix once you find it

Once you land on the right offset or delay value, write it down somewhere the next person running the booth will actually see it, a note taped to the encoder, a line in your run sheet, whatever sticks. The setting doesn't drift on its own, but gear gets swapped, cables get rerouted, and someone eventually undoes it without knowing why it was there. This is a one-time fix that becomes a recurring problem the moment nobody remembers it exists.

The gear-first instinct here is usually wrong

It's tempting to think a laggy stream means it's time for a better encoder or a faster computer. Almost every sync issue traces back to a setting, not a hardware ceiling, and chasing new gear before checking the offset values is spending money to solve a problem a few minutes with a stopwatch and a clap would've fixed for free.

Want to understand more of what's happening to your signal before it hits the stream? Check out our encoder basics post. And if this fixed a sync issue you'd been living with for weeks, grab the free Sunday Checklist to build pre-service habits that catch this kind of drift before doors open instead of mid-service.