Bluetooth audio delay (lip-sync issues on video calls) happens because Bluetooth adds latency when encoding and transmitting audio wirelessly. The delay is worse with the SBC codec and better with aptX or AAC. To reduce it: make sure your Bluetooth headset is using the "Hands-Free" or call profile (not the music/A2DP profile) during video calls. On Windows, go to Settings > Bluetooth & devices > your headset and check the connected services. Keep your headset close to your computer (within 3 feet) and remove obstructions. If the delay is still noticeable, switch to a wired USB or 3.5mm headset for calls — wired connections have near-zero latency. Some wireless gaming headsets use 2.4GHz dongles instead of Bluetooth, which have much lower latency.