others just changing to the H.264 format in max quality.
As I have no solution for your problem, as I do not use LR for video editing, I suggest that you do not rerender video files just to change the quality factor to a higher value. This will at the very most create a file taking more disk space but will not result in a higher quality! You need to film at the highest possible quality for getting most out of your data.
Sorry but that's not what I meant. I film in very high quality! I want to store all videos as H.264 format. Some files are simply being converted from MOV or other propriety formats.
That's indeed different.
Have you considered using Adobe Media Encoder or a similar tool to transcode the files into your target format? Lightroom is hardly designed for this kind of task.
This comes with a full CC subscription, but if you have the Photographers plan, you may not have access. You can download a free trial and see if it works for you.
Thanks but I have plenty of media encoders. I want to export from Lightroom: I export all images to one set of image folders and all videos from the same event to a parallel set of folders in a video folder with exactly the same structure. These are on different drives. So the Lightroom export is just a piece of housekeeping that I do after I have imported all my images and videos from a course onto my hard drive. Before doing that though I like to do a very quick trim of any excess stuff at the beginning or end, and just a bit of adjusting if its way too dark. So Lightroom would be ideal if it wouldnt keep freezing after the first export.