Between ExifTool and MediaInfo, I don’t know which is most reliable in extracting video metadata. All I do know is that based on user reports, ExifTool sometimes gets it wrong e.g. with Sony HV400 files. MediaInfo is not perfect either. Consequently Rapid Photo Downloader uses the output of both:
http://bazaar.launchpad.net/~dlynch3/rapid/zeromq_pyqt/view/head:/raphodo/metadatavideo.py#L144