I import a 3-hour video at 300Mb. I edit down the length a bit and try to export it at the same resolution (720p). At a bitrate of 5 Mbps, the predicted filesize is over 6 Gigs. Reducing the bitrate to 1 Mbps reduces the filesize to 1.5 Gigs. I attempted to export that last night with a predicted export time of 12 hours, it's now a third of the way done with 17 hours remaining. This is also the third time I've attempted to export this video, all previous exports have been incomplete, cutting off around the 2-hour mark.

What am I doing wrong? All the advice I can find online is about changing the bitrate, but that can't be all there is to it, because the edited the file is still several times larger than the longer video clip I started with.

EDIT: I restarted the export at 0.25 Mbps and now my export time is 29 hours for a 700Mb video.