I have been using Audacity for nearly 2 years. I do video game commentaries (oh the originality) so i use audacity to record the audio for the better clean up and such. Although in the video editing process i noticed the Audacity rendered mp3 is longer than it should. This has happened every time for as lng as I can recall and am only now coming to here. So I use Action! Mirillis as my video recording software but while i record the game I also record my voice on a third track so I may sync up my audacity audio file to the video easier. I usually sync it from the beginning but then when i reach around the middle or the end I notice that the Audacity audio file starts to sync off ahead of the Action audio file. So no longer are my words and video in sync. I am not sure what causes this either audacity records my speech an extra .01 second or that Audacity buffers for a second in a piece of the recording session and it counts that second as recorded audio. I am not sure what causes this or if it’s just an issue with my pc.
Depending on your microphone, the game timebase and the microphone timebase may simply be that far off. There aren’t liquid nitrogen cooled atomic clocks inside these things. I’d be surprised if they hit the nearest cycle at 44100 sample rate. And if they’re both off in different directions…
You can use Effect > Change Speed to sync them up again. If they’re always off the same amount, you should be able to carefully inspect a long show and get a very good correction value. “Voice is always off by 0.3% slow” for example.