How to time-lock high speed video and audio

Hello! I’m using the newest version of Audacity on a Windows 7 computer.
In a study, my colleagues and I are trying to use high speed video and a separate audio recording to document spontaneous vocalic interjections (e.g. Wow!, Ew!). We’re using a Phantom v. 7.3 camera and have been recording directly into Audacity using a uni-directional microphone while filming. Is there a way to get the video and audio feeds to sync up? We’ve rigged the camera to start recording when we push record in Audacity. To sync the two recordings, we’ve been using the clap method (by which I mean someone claps in front of the camera and we try to sync the beginning of the wave form with the visual of the hands coming together). The problem is that the audio recording registers the clap consistently between 165-175 ms behind the point the video registers the hands coming together. We’ve tried delaying the video recording for that length of time but to no avail. The audio is always behind the video. Any ideas?
I apologize if this is a rather stupid question or if it is covered elsewhere. I haven’t been able to find anything on it.

Sounds like a latency problem called “playthrough delay”.
You could try dialling-in negative 165-175 ms “latency correction” into Audacity Preferences

Otherwise using a video-editor where you can time-shift the audio backwards [relative to the video] that should be able to sync-up the audio & video.

NB: Using different devices to record audio & video can result the tracks slowly drifting out-of-sync because the internal clocks of the devices are not running at exactly the same rate , or because of occasional tiny pieces of audio or video “drop out” in one of the devices.

We tried the latency method you described. The weird part was that the effect didn’t disappear. It actually produced an additive effect. For example if we put -150 ms in, the next time the audio would be off by 300 ms. We tried putting in a positive number (150 ms) which didn’t help. We also tried delaying video recording on the camera. Nothing seems to be making a difference. We could always edit each file after we run our subjects, but that would be incredibly time consuming. We’re just looking for away around that if possible.

I thought the latency-correction would have fixed it. I was going to suggest trying another sound-recorder, like Window’s native one , but I just tried that and it has latency of about 200ms on my machine.

If you need to batch-process many audio files , (e.g. “trim” 150ms from the start on all the audio-files in a folder), there is a free program called SoX which will do that … SoX - Wikipedia