I have found for a few years now, that often when exporting a video, the audio ducking is out of sync from where I have keyframed it on the timeline. For example, the audio levels raise about a second too early before the narrator finishes speaking. I have had this issue again today on a very simple video with no audio effects added. I have tried exporting it as H264 and ProRes. Also exported it from Premiere, and in Media Encoder with the same outcome.
Any ideas why this may be happening? In the past I have had to export the video to find out where this issues happen, then bring the affected keyframes forward a second, so that it sounds correct in the next exported video.
I too am having this issue. But this is the first time. I am using .MTS files. I am wondering if that has anything to do with it because the files were not imported properly through media browser from the SD card and were out of sync. However they were put back into sync on the timeline. The Render our is in sync but the audio level keyframes are off by a second or more.