Sets an offset (in ms) for the automatic audio sync fix node
&sync=Xwill set an offset in milliseconds for the audio stream.
Tiny negative offsets may work, like
&sync=-25is possible, but large negative offsets will not work.
No clue if it is supported in OBS or not; works in Chromium/Chrome v76 or newer tho. Useful if the video device has a large delay that needs compensating for that isn't fixed automatically.