tabbles is also another interesting choice, but I don't think its been updated recently. And as I mention below, I would not be surprised to see a feature like this added to the OS possibly in the next release.
It should be noted that Apple's recent OS release has added tagging into the OS file system that works with its built in search tools. Why it is taking Microsoft so long to have done that as well is beyond me. Perhaps as always Microsoft will follow others lead and add it. I have not heard what might be coming in Windows 9 since 8.1 was just so recently released and with Ballmer leaving I not sure they know what they are doing next.
I think
MkvToMp4 is a really nice tagging program for video and author seems dedicated to keep updating it. What is really needed is an OS level tool in Windows that indexes file metadata and keeps track when files are moved and provides search tools on that metadata.