I recorded a vlog on my iPhone 8+ and edited it in iMovie. When I play the video in iMovie, the audio is perfectly fine and in sync with the video. However, when I export it and upload it to YouTube, the audio is completely out of sync and always starts at a certain time. I’ve done everything I could find to fix this issue yet it persists. I’m extremely desperate and I’m looking for a solution that does not include re-editing the entire clip.
I think I have a solution to your problem. I too was seeing this in iMovie and it turns out that if your audio track was sampled at 44.1 KHz, the export will likely mess up the audio sync. Fixing is quick and easy. Just take your audio track and resample it at 48 KHz. You can do this in a free tool like VLC. Then, bring in the new audio file, export your iMovie and it will work correctly.