Under "Segmented Video Upload Processing" they explain how cutting up the video before upload makes it easier to process. Does anyone know how they're maintaini

Under "Segmented Video Upload Processing" they explain how cutting up the video before upload makes it easier to process. Does anyone know how they're maintaining audio sync? Every single time I've tried to cut up (mp4/m2ts) video to re-encode it in parallel, I've had it go completely out of sync.