If you clicked the Get MP4 button in the old version, it would do one of two things. For an unedited video, it would simply take you to the file that was saved at the end of the recording session. For an edited video, it would render a new copy of it (just opening the edited video in FBX itself, does not require the video to be re-rendered).
If it was only taking a few seconds, then it wasn't doing any rendering because it is simply not possible to do it that quickly - rendering is a slow process and there's not much we can do about that. Presumably you were just going to the original video rather than rendering.
This inconsistency in what the Get MP4 button did, was causing some confusion for some users so we've tried to make things more transparent - it is now an export button that will always render a new copy of the recording. If you want the original video file, just grab it from your captures folder.
