Explain how well synced audio & video recorded in XProtect is. Second, if audio is recorded externally with a sync track, and recorded video is pulled from XProtect via the API, how can the external audio be properly sync'ed with the video.

Please read this explanation, I hope it would be helpful.

https://developer.milestonesys.com/s/article/Audio-and-video-are-out-of-synchronization