Video encoding for archival

"H.264 is the current state-of-the-art codec, will give you the best quality/size and will likely be in use for some time.

Ogg Theora is not as powerful as H.264, but is completely open and doesn't have the patent questions that H.264 has (link). Theora is also being used by Firefox for the HTML5 element, so it will probably stick around for a while.

Dirac is another codec you might consider. Like Theora it is an open standard, but aims to have quality comparable to H.264. It is being actively developed by the BBC, but is not yet in widespread use.

There's no one best answer, but for good quality and future use I would choose one of these three. At this point I would only use XviD if I needed to play the video on legacy devices."

"I wouldn't worry about the format too much. If all else fails, mplayer and VLC will be around in 15 years (being a very prevalent open source projects)

Obviously don't use an obscure, application specific format.. H.264, Theora, MPEG-4, XviD etc should be fine. You can always reencode the data should a better suited codec appear in the next decade or two..

The thing to worry about is the data storage, if your storage dies, or the files become corrupted, the codec is irrelevant. Every few years you should really transfer the files to new storage (which will be come easier as drives get bigger/cheaper), when you do that, check the files are still playable with current software/codecs.

If you're really paranoid, you could store a copy of the transcoding software (say mplayer/mencoder), and an operating system disc (a linux distribution?) - then if somehow h.264 becomes impossible to play, you create a virtual machine, install or compile the transcoding application and convert the files to something playable.. You can still emulate Windows 3.1 in VMWare, so you should be able to emulate the current Linux distros in a few decades (assuming no nuclear apocalypses)"