With a relatively clean install of Windows 8 all the AVI files included with games just play sound. I'm guessing it's a missing codec but searching the site and wiki didn't turn up any info and installing the games also didn't seem to help. Does anyone know the particulars of what video encoding is used?

I'm a Windows 7 user, but regarding missing codecs I use only ffdshow and xvid. They are perfectly safe and well known so you may download them and instal to see if they solve your problem.

ffdshow (download both 32 and 64 bit versions) - http://www.free-codecs.com/FFDShow_download.htm
xvid 1.4-127 x86 & x64 - http://www.free-codecs.com/xvid_codec_download.htm

If yoy are looking for a media player I recomend Media Player Classic - Home Cinema:

http://www.free-codecs.com/Media_Player_Classic_Home_Cinema_download.htm

Grab the K Lite codec package, that way you can just use media player for the files :

http://codecguide.com/

Latest version of the Codec Pack version 9.4.0 supports Windows 8

I second K-Lite. Don't listen to all those "don't download the pack, it makes mess!" people. Such arguments are out of date since windows 98.

Btw. in some old games you still may get no video at all. Mostly because old games use very old codecs that are not used anymore.

Depends a bit actually. While there is nothing inherently wrong with packs, they can cause some issues with certain games. Thief being a prime example of a game that (at least if you play the original version) don't play nice with the K-lite codec pack, or rather some of its components.

I use CCCP codec pack myself.
It also comes with Media player classic bundled.

Grab it here.

Personally, I think VLC is the "should all else fail" option as it is not exactly perfect (have you seen how blocky it can make certain videos?).

I'm personally giving "Media Player Classic - Home Cinema" a try and it seems flawless as far as I can tell, and free software to boot, the only issue being development was discontinued 6 years ago.

I guess it's really all down to personal preference though, I used VLC as my main player for quite a while and it seemed fine to me at the time.

True. You need to download a specific version of codecs for some games. That's one of the charms of retro gaming.

?
New version released 1 month ago
http://mpc-hc.sourceforge.net/

And now I feel silly. Looks like I didn't have my eyes open when I installed it and blindly accepted what I just read on Wikipedia.

Thank you kind sir! I had no intention of misleading anybody. Honest!

Edit: I realise this kind of goes against my forum title so I have modified it accordingly.

Edit2: I feel even more silly now I realised it was purely user error: I was looking at the wrong part of the article

If you want to play the videos of your games while you play them and you have problems during the games, all the posts above mine are valid. The packs will install the codecs so your system will use them. If you just want to play the videos, you could install PotPlayer. It's an excellent video/multimedia player (the best I have used so far, and I have used most all of them -including VLC-). Also, you won't be needing to install extra codecs or packs, because the player have them (built-in codecs).

Yes, and some codecs conflicts with others, which is the main issue with Thief. So even if you have the right codec installed, the K-lite pack still needs to be uninstalled for Thief to run properly.