Can someone suggest a workflow for transcoding videos in iPhoto from Motion-JPEG to something smaller?

Question

I've shot a lot of video with "still" cameras over the years, and a lot of it is encoded with Motion-JPEG, which uses a lot of disk space per minute of video, compared to more efficient codecs such as H.264 or AVCHD, etc.

I'm not asking about the actual conversion, I know I could figure that out with ffmpeg or something like that. What I'm concerned about is converting the files but keeping them in-place in my iPhoto library, with all metadata intact. And even if there's a way to do so manually, that'd take way too much time — I need a way to automatically transcode Motion-JPEG videos "in place" without losing metadata.