Capture Card Audio Out of Sync in OBS: Fix

Audio is off by the same amount all the time

1. Open Edit → Advanced Audio Properties in OBS.
2. Find the capture card's audio (or the Audio Input Capture you use for it) and enter a Sync Offset in milliseconds. Start around 100–200 ms; some cards need more. Plugable, for example, suggests about 470 ms for one of its cards.
3. Record 20 seconds while clapping in view of the game or a webcam, play it back, and adjust in 20 ms steps.

OBS can only delay audio. If the audio comes after the picture, delay the video instead with a Video Delay (Async) filter, or delay everything else by the same amount.

The gap grows the longer you stream

• In the Video Capture Device's properties, set Use buffering to Disable. With buffering on, video often drifts behind over time.
• Set OBS to 48 kHz (Settings → Audio) and set the capture card's audio device to 48 kHz in Windows sound settings too.
• Use the capture card's own audio, not game sound coming from another device: two clocks drift apart.

Your webcam or mic is behind the game

Low-latency cards can be faster than a webcam. Add a sync offset to the mic and a Video Delay filter to the game capture rather than the other way round.